Everyday Science — Chapter 7

Chemistry in Daily Life — Elements and Symbols, Acids Bases and Salts, Metals and Alloys, and Common Chemicals

Why this chapter matters: chemistry is the most definition-dense block in Everyday Science after physics — the papers rarely ask for equations, but they ask the same definitions, symbols, formulas and everyday uses again and again. Our verified banks hold 192 questions matching this topic by question text, and the weight sits almost evenly across it: elements, atoms and the periodic table (48 questions) — above all the most abundant element in the universe, in the crust and in the air, radioactivity and its discoverer, symbols and halogens — metals, non-metals and alloys (46) — alloy compositions, the liquid metal, the best conductor, the most malleable metal and rusting — organic, industrial and common chemicals (41) — coal types and deposits, natural gas, soap, cement and combustion — gases, water and states of matter (34) — carbon monoxide, the ozone layer, laughing gas, evaporation and the freezing point of water — and acids, bases, salts and pH (23) — the car-battery acid, table salt, rock salt and the salt-water lake. The chapter is built on Lecture 10 (Muhammad Adnan), whose definitions and values are the papers’ own language; bank-only facts (Becquerel and Villard, tungsten as the hardest metal, argon in bulbs, oxygen at 65% of the human body) are added where the lecture is silent and flagged as such in Section 8. Measuring instruments get their full tables in Chapter 8 (Inventions, Discoveries & Instruments) — here they appear only where the chemistry needs them.

1. What chemistry studies — matter, mixture, compound, molecule

• Chemistry is the branch of science dealing with the composition, structure, properties and reactions of matter.
• Organic chemistry is the study of carbon, hydrogen and their derivatives. Inorganic chemistry is the study of all elements and their compounds except carbon, hydrogen and their derivatives. Environmental chemistry is the branch dealing with chemical and other pollutants in the environment.
• The scope the papers ask: petroleum (gas, petrol, diesel), petrochemicals (for example PVC — polyvinyl chloride pipes) and the pharmaceutical industry.

2. Sub-topic 1 — Elements and symbols: the atom and the periodic table

Elements: how many, and which ones are radioactive

• 118 elements have been discovered; 92 occur naturally.
• Modern definition: an element is a substance made of the same type of atoms that cannot be decomposed into simpler substances.
• Elements above atomic number 82 are radioactive — the tricky, repeated MCQ. Examples: uranium, plutonium — plutonium is used as fuel for nuclear fission reactions, and the fuel in a fast breeder reactor is uranium–plutonium oxide. Radioactivity is measured by the Geiger counter (bank fact, asked directly). Radioactivity was discovered by Becquerel and gamma rays were discovered by Paul Villard (bank facts, not in the lecture).
• About 80% of all elements are metals.

Symbols and valency

• Symbols were suggested by Berzelius: Fe = iron, Cu = copper, H = hydrogen, O = oxygen — and the banks add K = potassium (symbol question, bank answer) and Ga = gallium.
• Valency is the unique property of an element — it depends on the electrons in the outermost shell. Hydrogen = 1, carbon = 4, oxygen = 2.

Atomic number, mass number, and the particles

• Atomic number = number of protons, represented by Z, discovered by Moseley. Mass number = protons + neutrons in the nucleus, represented by A. In a neutral atom, atomic number = number of electrons, and an atom’s position in the periodic table is fixed by its proton number. Worked bank type: a cation with +1 charge and 10 electrons has 11 protons.
• Proton discovered by Goldstein in 1886; mass = 1,840× the electron; positive charge. Electron discovered by J. J. Thomson — Nobel Prize 1906 for the discovery of the electron and conduction of electricity in gases; negative charge. Neutron discovered by Chadwick in 1932. Sir William Crookes — British chemist — Crookes tube.
• Electron movement: lower → upper shell = absorbs energy; upper → lower = radiates energy. Adding electrons gives a negative charge; removing electrons leaves a body positively charged.
• Sun’s spectrum = band spectrum. Paschen series lines are in the infrared. Infrared waves have a longer wavelength than red light. X-rays are produced when a stream of electrons in an X-ray tube strikes a metal target. A cyclotron is used to accelerate a beam of charged particles. Atomic theory — all matter composed of discrete units — was first suggested in ancient Greece, later by John Dalton (19th century).

Isotopes and allotropy

• Isotopes = same atomic number, different mass number (same protons, different neutrons). Hydrogen’s three: protium, deuterium, tritium — ¹H₁, ²H₁, ³H₁. Heavy water = D₂O. Uranium isotopes: U-234, U-235. ¹H₁ has 1 electron, 1 proton, no neutron; deuterium differs from hydrogen in having a neutron.
• Allotropy = the existence of an element in more than one form in the same physical state. Carbon’s allotropes: diamond, graphite, buckyballs. Diamond is a form of carbon (bank question) and the hardest naturally occurring substance (PMS Screening 2026 GK Grand Mock 20, Q34; bank-attested — 4 exam-paper rows plus practice-set rows — but below the 5-paper limb, so no mark claimed); ozone is the allotropic form of oxygen — 3 oxygen atoms.

Electronic configuration

• Electronic configuration = the distribution of electrons in orbitals by increasing energy. Energy levels n = 1, 2, 3…; shells K, L, M, N — K closest to the nucleus.
• Electrons per shell: 2n² — K = 2, L = 8, M = 18, N = 32. Subshells: s = 2, p = 6, d = 10, f = 14. Filling follows Hund’s rule.

Chemical bonds and radioactivity’s three rays

• Ionic bond = complete (100%) transfer of valence electrons. Covalent bond = mutual sharing (50/50) of electrons.
• Radioactivity = the property of atoms with an unstable nucleus — it breaks down naturally giving rays, particles and large energy.

The periodic table and its families

• Horizontal rows = periods, vertical columns = groups. Periodic law (modern): properties of elements are a periodic function of their atomic numbers; Mendeleev’s version used atomic masses — know the difference.
• Mendeleev — Russian chemist — 1869 — arranged 63 elements in order of increasing atomic mass. 1st period = short period (only 2 elements: hydrogen, helium); 2nd and 3rd = normal periods; 6th and 7th = very long periods. Elements of a group have a collective name = family.

3. Sub-topic 2 — Acids, bases, salts and pH

Tests first: taste, litmus, and the common element

• Acids: sour taste (unripe citrus fruit, lemon juice); turn blue litmus red; the element common to all acids = hydrogen (proton). Examples: HCl, chloric acid, nitric acid, sulfuric acid. An acid is neutralized by an alkali/base.
• Bases: bitter taste; slippery feel — soap is a base, slippery to touch; turn red litmus blue; all bases contain the hydroxyl group.
• pH scale range = 0–14; 7 = neutral. Adding alkali to an acidic solution increases pH.

Uses the papers ask

• Sulfuric acid in batteries — the banks’ car-battery acid question. Nitric acid in fertilizers, explosives, paints, drugs. Acids are used for etching designs on copper utensils.
• Calcium hydroxide (lime water) — manufacture of bleaching powder, softening of hard water. Ammonium hydroxide (ammonia water). Magnesium hydroxide = milk of magnesia — neutralizes stomach acidity.

Salts, neutralization, and the named salts table

• Salts = ionic compounds — formed by neutralization of acid and base → salt + water; the reaction name is the neutralization reaction. Amphoteric species act as both acid and base — for example water.
• Fresh egg sinks in pure water but floats in saturated salty water — due to the higher density of salty water.
• NaCl = table salt / common salt; used to make washing soda and caustic soda; the most common salt = sea salt; common salt mixed with ice lowers the freezing point.

Lime water, soda water, and the salt the banks count

• Soda water is carbonated by adding CO₂. CO₂ passed through lime water: the liquid first turns cloudy white, and on long passing the cloudiness disappears due to water-soluble calcium bicarbonate.
• Hardness of water is due to dissolved salts (the banks’ hardness question). The most common salt in seawater is common salt (NaCl); rock salt is Pakistan’s deposit the banks ask twice — the biggest rock-salt deposits in Pakistan and their annual production are both bank questions, and a salt-water lake in Balochistan is asked by name.
• Sulfuric acid and nitric acid were discovered by Jabir ibn Hayyan (Jabar Bin Hayyan) (bank question, asked twice with both spellings).

4. Sub-topic 3 — Metals, non-metals and alloys

What a metal is

• All metals have lustre/shine, are malleable and ductile (can be drawn into wires), are good conductors of heat and electricity, and form positive ions.
• Most metals are solid at room temperature — except mercury (Hg), which is liquid. Best conductor among metals = silver; copper is used for wiring because it is cheaper. Gold = first metal discovered by man and the most malleable metal. The hardest metal is tungsten (bank fact, not in the lecture). The most abundantly found metal on the Earth’s surface is aluminium; the second most abundant metal is iron (bank fact, confirming the lecture’s crust table).
• Earth’s crust: oxygen 47%, silicon 28%, aluminium 7.8%, iron 5%. Most abundant metal in the Earth’s crust = aluminium. Ocean: oxygen 86%, hydrogen 11%, chlorine 1.8%. Atmosphere: nitrogen 78%, oxygen 21%, argon. Most abundant elements overall: universe = hydrogen, crust = oxygen, atmosphere = nitrogen, human body = oxygen (65%) — four different answers, and the banks ask all four (see Traps).

Individual metals and minerals

• Aqua regia dissolves platinum. Aluminium ore = bauxite (appeared in an EST paper). Ruby and sapphire = aluminium oxide.
• Liquid sodium is used as a coolant in nuclear reactors. Mica = good conductor of heat but an electrical insulator — used in transformers and capacitors. Zirconium is essential for nuclear reactor construction. Quartz mineral = most resistant to chemical weathering. Dolomite is an ore (bank question). Copper, gold and silver deposits discovered in the late 1990s and bauxite localities are bank questions in this block.
• Ores = کچی دھاتیں. Radium is extracted from pitchblende (naturally radioactive). Most ores contain oxygen and sulfur.

Mineral uses — the table the papers draw from

Exam Trend for this table: 🔁 Most Repeated, ⭐ Must Know. The mineral-use family is asked as a family across the banks, not as one-off facts: 56 unique stems across 32 bank files, including 25 distinct exam-paper files (FPSC 2001–2016, PPSC 2019–2026) — counted from the full bank set (594 files / 56,922 questions, script hidden_files/goldmine-notes-count-mineral-uses.py, dump hidden_files/goldmine-notes-mineral-uses-dump.json). ⭐ because it is still asked in 2025–2026 papers: graphite in pencils (PPSC Assistant Punjab Police 2026), quartz formula SiO₂ (two PPSC PMS papers 2026), aluminium obtained from bauxite ore (PPSC Assistant PESSI 2025), graphite as the conducting non-metal (PPSC Field Officer 2025). No 🆕 claim — the family has been asked since 2001. The CSS-MPT 1000-booklet Q101–200 contributes 19 of the rows (feldspar, bauxite, hematite, galena, graphite, gypsum, fluorite, kaolin, apatite, asbestos, quartz, mica, gemstones); the rest is exam-paper material. Rows already taught above (mica, quartz weathering, ruby/sapphire as aluminium oxide, gypsum as non-metallic) are repeated here so the table is complete in one place.

Alloys — the composition table the papers repeat

• Alloy = mixture of metals (or metal + other elements) in the molten state — Urdu: بھرت.

Ores, extraction and everyday materials — the mock’s missing rows

This section is a coverage-audit fold-in (2026-11-03, PMS Screening 2026 Physical Science subject mock, 100 items, Sir Adnan booklet ‘PMS GK Physical Science Mock Test’): the mock’s items were chapter-checked against this chapter and the rest of the Everyday Science chapters, and the rows below are the genuinely missing core — the copper and zinc ores, gold extraction, open-cast mining, plain steel, glass from sand, and the LPG expansion. Items already taught elsewhere are cross-linked, not repeated: the Section 4 mineral-uses table above (bauxite→aluminium, hematite→iron, galena→lead, quartz→glass optics); the alloys table above (stainless steel = iron + 10–12% chromium); sedimentary rocks as the coal/petroleum host (EDS-02); fractional distillation and LPG = butane + propane (Section 6); natural gas = methane (Section 6); acid-rain gases and the greenhouse effect (Section 7); alpha = helium nucleus and gamma = highest penetration (Section 2). No 🔁/⭐/🆕 mark is claimed for this section: the bank-evidence script below finds the families thin in exam papers (chalcopyrite 1 row, zinc blende/sphalerite 1 row, cyanide process 0 rows, open-cast 1 loose row, steel iron+carbon 1 row, glass-from-sand 1 genuine row, LPG expansion 2 genuine rows, over 608 files — script hidden_files/goldmine-notes-count-eds07-physmock.py) — the section is mock-led teaching material, taught as standard definitions, not as a paper-repeater. BankCount stays 192.

• Mining itself is the process of extracting minerals from the Earth — the mock asks it twice (as “minerals are obtained by” and as “the process of extracting minerals”), and both answers are the same word.

Non-metals, metalloids, and the exceptions

• Non-metals are non-lustrous; solid non-metals are brittle — they break into pieces on pressure (“brittle” is the MCQ word). Non-metals are poor/non-conductors of electricity; they gain electrons → form negative ions, while metals donate electrons → positive. All gases are non-metals.
• Sulfur is used in a beauty parlour for hair setting (bank question, asked directly). Bromine = the non-metal that remains liquid at room temperature — poisonous. Graphite = a non-metal AND a conductor — the exception that breaks the “non-metals don’t conduct” rule. Gypsum = non-metallic mineral — plaster of Paris is obtained from gypsum.
• Metalloids = elements with intermediate properties of metals and non-metals — located around the diagonal line from boron to astatine (except aluminium) in the periodic table. Silicon, the metalloid the banks name most, is the element required for solar-energy conversion (asked three ways) — it is also the semiconductor material of Chapter 6, not a conductor.

Corrosion, rusting, electrolysis and redox

• Corrosion = slow eating away of metal by the surrounding medium — the general term. Rusting of iron = the most common example of corrosion. Rusting needs moist air; during rusting iron gains weight. Oxalic acid solution removes rust stains on cloth.
• Aqueous CuSO₄ solution is acidic. Metals are deposited at the cathode because the cathode supplies electrons. NaCl in water → sodium and chloride ions separate. Nickel and cadmium are used as the electrode pair in rechargeable batteries (torch light, electric shaver). A secondary cell can be charged again. Electrolysis of brine produces (bank question) the chlorine/sodium-hydroxide pair of the chlor-alkali set.
• Galvanizing = applying a protective zinc coating to steel/iron to prevent rusting; the most common method is hot-dip galvanizing. For galvanizing iron, zinc is the metal used (bank question).
• Redox reaction = oxidation + reduction simultaneously. Oxidation = addition of oxygen / removal of hydrogen (“oxy-addition”); rusting of iron involves oxidation and bleaching by chlorine is oxidation. Reduction = the reverse.

5. Gases, water and states of matter

Gases: behaviour and laws

• Gases have no definite shape and volume; their intermolecular forces are very weak. Pressure is a significant property of gases. With increase in temperature, viscosity of gases increases (liquids decrease). When a gas is compressed, its internal energy, kinetic energy and absolute temperature increase. Boltzmann constant = universal gas constant ÷ Avogadro’s number. A gas liquefies by pressure when its temperature is below its critical temperature.
• Boyle’s law: temperature constant; volume and pressure inversely proportional — pressure ↑ → volume ↓. Charles’s law: pressure constant; volume and temperature directly proportional.

The gases the papers name, one by one

• Hydrogen: lightest of all gases; combustible (can blast). Most abundant element in the universe. Used in the manufacture of vanaspati ghee; causes minimum environmental pollution; has the highest fuel value. The Sun is mainly composed of hydrogen. A hydrogen balloon rises in air because it is lighter than air.
• Helium is used in balloons; a noble gas — it does not burn. Argon (with nitrogen) is used in electric bulbs (bank question: the inert gas commonly used in a bulb is argon; the lecture teaches nitrogen + argon together).
• CO₂ = greenhouse gas; used in soft drinks (carbonated drinks are made with chilled water — cold water attracts more CO₂); the gas used in fire extinguishers is carbon dioxide (the lecturer flags this as the tricky MCQ with near-about options); CO₂ mainly causes global warming. The largest emitter of carbon dioxide in the atmosphere and the carbon dioxide inhaled in air (approximately) are bank questions in this block; the planet containing the largest quantity of carbon dioxide (95%) is Venus (bank question).
• CO = poisonous gas — present in car/vehicle exhaust; produced when coal burns without enough air/oxygen (for example a heater in a closed room in winter). Carbon monoxide has a stronger affinity to bind with haemoglobin in blood than oxygen does (bank question).
• Chlorine is used to kill bacteria in water (water purification); it is a bleaching agent; the process is chlorination (appeared in a PFSA paper).
• Laughing gas = N₂O (nitrogen + oxygen). Nitrogen + argon are used in electric bulbs.
• Oxygen helps in burning (no fire without it); paramagnetic. Rocket fuels: liquid oxygen, nitrogen tetroxide, hydrogen peroxide. Divers use oxygen + helium as an artificial atmosphere.
• Fluorine = most reactive (element, as well as halogen). Ammonia is lighter than air; used in refrigerators / cold storage; it is a base. Radon is produced in unventilated rooms.
• Evaporation causes cooling — after bathing, the fan feels cool because high-energy molecules evaporate, taking heat from the body. Condensation = converting gas to liquid. The first molecule discovered in space was the hydroxyl (OH) radical (bank answer).

Solids, liquids, and pressure

• Solids: definite shape; atoms closely packed; rigid; denser than liquids and gases; exist in amorphous or crystalline form. Liquids: strong intermolecular forces; definite volume; NO definite shape — they take the shape of the container.
• Food cooks quickly in a pressure cooker because the boiling point of water is increased. Capillary action: oil rises in an oil-lamp wick; blotting paper absorbs ink. Water boils below 100°C at higher altitude because atmospheric pressure is lower than at sea level.
• Atmospheric pressure = 760 torr; at sea level = 1013.25 millibars ≈ 17.7 pounds per square inch. SI unit of pressure = pascal. Pressure decreases climbing a mountain; going upwards, atmospheric pressure decreases (bank question). Wind blowing in a spiral around a low-pressure region is a cyclone — cyclones are low-pressure systems of winds.

Water: the compound the papers test hardest

• Water is a compound of only two elements: oxygen + hydrogen. Breaking water into H₂ and O₂ is decomposition — it needs very high energy, so it is not used. Water is the universal solvent.
• Pure water: clear, colourless, odourless, tasteless; neutral to litmus — pH 7; specific gravity = 1. Water drops are spherical because of surface tension. Freezing point = 0°C (freezing and melting point are both 0°C — the tricky MCQ). Maximum density (1 g/cm³) at 4°C; heated from 0→10°C, its volume first decreases then increases. Dielectric constant of water = 80 (at 18°C). As the temperature of water rises, its surface tension decreases (bank question).
• Heavy water D₂O is used as a moderator in atomic reactors; its freezing point is 3.82°C. Soft water produces good lather with soap; hard water does not.
• A water molecule has 2 hydrogen atoms and 1 oxygen atom (bank question). The freezing point of water in Fahrenheit is 32°F (bank question, the companion to 0°C).
• Filtration (using filter paper) separates solid from liquid — for example sand from water. Distillation separates salt + water (both recovered); contaminated water is purified by distillation — and salt is removed from water by distillation (bank question).
• Salinity of sea water = the amount of common salt (NaCl) in 1 kg of sea water. Most abundant elements in sea water = sodium and chlorine. The purest form of water is obtained from rain (bank question, asked twice); rain water = purest form of water.

Thermometry

• 0°F = −18°C (rounded, as taught). Human body temperature is measured in Fahrenheit. The most suitable thermometer for the boiling point of water is mercury. Know the conversion formulas between Fahrenheit, Celsius and Kelvin — MCQs come from them.

6. Sub-topic 4 — Common chemicals: organic, industrial and everyday chemistry

Hydrocarbons and natural gas

• Alkanes = saturated hydrocarbons — single sigma bonds only (no double, no triple). Alkenes (double bond) and alkynes (triple bond) = unsaturated.
• Natural gas = methane, CH₄ — an alkane (saturated); structure: 1 carbon, 4 hydrogens (ratio 1:4); methane = gobar gas / biogas. Biogas is a mixture of methane and carbon dioxide (bank question, in the gases bucket). Natural gas was discovered in 1952 (bank question); the province that is the largest producer of natural gas and the country that is the world’s largest natural gas producer are bank questions in this block.

Coal: formation, types, and Pakistan’s deposits

• Coal = blackish complex mixture of compounds of carbon, hydrogen, oxygen + small amounts of nitrogen and sulfur; the most common and popular industrial fuel. Wood → coal conversion = carbonization. Long chain of carbon = catenation. Coke is made by heating coal in absence of air at 1300°C.
• Types, in ascending quality and carbon percentage — learn them as a ladder:

• Pakistan’s coal: the largest coal resource / biggest deposits of coal in Pakistan (Thar coalfields, Sindh — over 185 billion tonnes estimated, including the Thar identified figure), the province that is the major coal producer, how much coal is used for thermal power vs brick kilns, and how many thermal power stations use coal are all bank questions in this block. Coal is the remains of plants (bank answer to “coal is the remains of…”) and over 90% of coal is used in the electricity sector in one bank key.

Petroleum, urea, and the first organic compound

• First process in petroleum refining = distillation — fractional distillation. LPG = butane + propane. Gasoline quality is checked by octane number. Crude oil is heated in a furnace up to 400°C. Pitch is produced from petroleum. The sector that is the biggest consumer of petroleum products in Pakistan is a bank question here.
• Urea was prepared by Friedrich Wöhler (German chemist) in 1828 — name + year asked; it was the first organic compound synthesised in the laboratory, ending the myth that organic compounds occur only naturally. (The banks’ “where is urea formed in the human body” question is biology — the liver — and belongs to Chapter 3’s body block, not to Wöhler’s synthesis.)

Polymers, alcohols, benzene

• Polymerization = union of two or more molecules to form a large single molecule (polymer). PVC = polyvinyl chloride (plastic). Nylon is non-biodegradable; rayon = artificial silk (very important MCQ). The process of union of two or more molecules into a large single molecule is the banks’ polymerisation question (counted in the gases bucket by first-match).
• Ethanol (ethyl alcohol): used in spirit lamps; most common in all perfumes; antifreeze for automobile engines; anti-knock compound TEL = tetraethyl lead. Ethene gas = artificial ripening of green fruit. Benzene: empirical formula CH, molecular C₆H₆. Nickel catalyst converts oil into ghee (vanaspati). Combustion = other name of burning. Asbestos = fire resistant. Grignard reagent is the named organometallic reagent of the organic block. Hydrogenation = addition of hydrogen; cooking oil → vegetable ghee by hydrogenation. Gas required for combustion is oxygen (bank question).

Soaps, fertilisers, cement and paper — the common chemicals themselves

• Saponification: triglyceride + NaOH/KOH (bases) → soap; caustic soda (NaOH) is extensively used for making soap. Soap is made by saponification (bank question); what soap is, chemically, is the banks’ follow-up question — a sodium/potassium salt of a fatty acid, the product of saponification above.
• Fertilisers: potassium nitrate is a fertilizer (Section 3); nitric acid is used in fertilizers; the fertilizer company of Pakistan that can produce 34% nitrogen fertilizer is a bank question in this block. Chile saltpetre (NaNO₃) is the nitrate fertilizer of Section 3.
• Cement industry raw material = limestone (calcium carbonate); the largest quantity used is calcium oxide. The raw material used for the manufacture of glass and cement is the banks’ joint question, and for the manufacture of cement, calcium oxide/limestone is used in the largest quantity (bank question, asked twice).
• Paper industry: newspaper can be recycled 5 times; poplar wood as raw material.
• Bleaching powder loses power on long keeping (→ calcium chloride + calcium chlorate). Bleaching powder itself is made with calcium hydroxide (Section 3).
• Heat, energy, nuclear (lecture close): unit of heat = joule. Blue flame hotter than red flame. Boiling of egg = chemical change. Molecules of high energy control the chain reaction in a nuclear reactor; the energy required to break a nucleus is binding energy. A nuclear bomb / reactor produces heat through a chain reaction.

7. Environmental chemistry — smog, acid rain, ozone, greenhouse

• Smog (≠ smoke) = great danger — reduces visibility, hurts eyes, causes disease when breathed, obstructs UV rays, damages property and vegetation. Smog, NO₂, SO₂ and dust are the source of (bank question) the urban air-pollution block; in industrial cities with smoke-fog (smog) most of the time at night or in the mornings, the death rate appears high on account of the smog itself (bank question).
• Acid rain = high levels of sulfuric and nitric acid; a cause of soil pollution.
• Ozone = allotropic form of oxygen — 3 oxygen atoms; CFCs (chlorofluorocarbons) cause ozone-hole depletion. An international treaty signed in 1987 related to protecting the ozone layer by phasing out ozone-depleting substances is the Montreal Protocol (bank question — the 1987 treaty, the year the banks ask). The ozone layer lies in the stratosphere, about 30 miles (50 km) above the Earth (bank question); it protects the Earth from ultraviolet rays and prevents ultraviolet radiation from entering the atmosphere (bank questions, asked three ways); the gas that affects the ozone layer is the CFC group.
• Greenhouse effect = air absorbs long heat waves from Earth after letting short waves from the sun pass; main greenhouse gases = CO₂ and methane; global warming is caused by CO₂. The primary component of greenhouse gas contributing to global warming is carbon dioxide (bank question).
• Most serious effect of hazardous waste = contamination of groundwater; pesticides and fertilizers wash into water channels — a cycle back to our use. Aerosols = air pollution. Climate: the two most important factors are temperature and precipitation. Weathering = decomposition of rocks. Clouds = collection of water droplets suspended in air. If there was no CO₂ in the Earth’s atmosphere, the temperature of the Earth’s surface would fall (bank question — the greenhouse blanket removed).

8. Master tables — the whole chapter on two tables

The atom, the table, and the tests

Alloys, coal, and everyday chemicals

9. Rapid-fire one-liners

• Chemistry = composition, structure, properties, reactions of matter; organic = C, H + derivatives; inorganic = all except C, H + derivatives.
• Matter = occupies space + has weight (air too); mixture = physical, no fixed ratio, properties retained; compound = fixed ratio by mass, properties change; homogeneous = ice cream, heterogeneous = soil/rock.
• Molecule = smallest independent particle; mono/di/tri-atomic; homo = ozone, hetero = H₂SO₄.
• 118 discovered, 92 natural; above Z = 82 = radioactive; Geiger counter measures radioactivity; radioactivity discovered by Becquerel; gamma rays by Villard.
• Symbols by Berzelius: Fe/Cu/H/O/K; valency = unique property (H = 1, C = 4, O = 2), outermost electrons.
• Atomic no. = protons = Z (Moseley); mass no. = p + n = A; cation +1 with 10 e⁻ → 11 protons.
• Isotopes = same Z, different A; H: protium/deuterium/tritium; D₂O = heavy water; U-234/235; allotropy = same state, multiple forms (diamond, graphite, buckyballs).
• Goldstein 1886 proton (1,840× e⁻); Thomson electron (Nobel 1906); Chadwick 1932 neutron; Crookes tube.
• Rows = periods, columns = groups; modern law = atomic numbers, Mendeleev = masses; Mendeleev 1869, 63 elements (Russian).
• 1st period = short (H, He); 6th/7th = very long; group collective name = family.
• IA alkali, IIA alkaline earth, VIA chalcogens, VIIA halogens (F, Cl, Br, I), 0/8A noble; F most reactive halogen, At least; noble = inert, highest ionization potential.
• Shells K2 L8 M18 N32 (2n²); subshells s2 p6 d10 f14; Hund’s rule.
• Ionic = 100% transfer; covalent = sharing; alpha = He nucleus (2p+2n); beta = fast electrons; gamma = EM waves, bomb blast, DNA damage.
• e⁻ lower→upper absorbs, upper→lower radiates; sun spectrum = band; Paschen = infrared; X-rays = e⁻ stream hits metal target; cyclotron = accelerates charged particles.
• Crust: O 47%, Si 28%, Al 7.8%, Fe 5%; top metal = aluminium; ocean: O 86%, H 11%, Cl 1.8%; air: N 78%, O 21%; 80% of elements = metals.
• Metals: lustre, malleable/ductile, conductors, +ions; Hg = liquid metal; Ag = best conductor; gold = first discovered, most malleable; tungsten = hardest (bank).
• Aqua regia → platinum; bauxite = Al ore; ruby/sapphire = aluminium oxide; liquid Na = reactor coolant; mica = heat conductor, electrical insulator; zirconium = reactors.
• Alloy = molten mixture (بھرت); German silver = Cu+Ni(+Zn); brass = Cu+Zn; solder = Sn+Pb; bronze = Cu+Sn (control valves); phosphorus bronze = springs; ferrosilicon = Fe+Si.
• Ores & extraction (mock fold-in Section 4): chalcopyrite = copper ore (CuFeS₂); zinc blende/sphalerite = zinc ore (ZnS); gold = cyanide process; open-cast mining = large open pits; plain steel = iron + carbon; glass = sand (SiO₂); LPG = Liquefied Petroleum Gas.
• Non-metals = non-lustrous, brittle, poor conductors, gain e⁻ → −ions; all gases = non-metals.
• Sulfur = beauty parlour hair setting; bromine = liquid at room temp, poisonous; graphite = non-metal conductor; gypsum → plaster of Paris.
• Metalloids = intermediate, diagonal boron→astatine (except Al); silicon = solar-energy element.
• Gases: no shape/volume, weak forces; viscosity ↑ with T; compression ↑ internal/kinetic energy, T; Boltzmann = R/Nᴀ; evaporation = cooling; condensation = gas→liquid; liquefy below critical T.
• H₂ = lightest, combustible, most abundant element; vanaspati ghee, min pollution, highest fuel value; sun = H; isotopes P/D/T; ¹H₁ = 1e⁻, 1p, 0n.
• He = balloons, noble, no burn; CO₂ = greenhouse, soft drinks (chilled water), fire extinguisher, global warming; CO = poisonous (exhaust, closed-room heater); Cl₂ = kills bacteria, bleaching, chlorination; N₂O = laughing gas; N₂+Ar in bulbs.
• O₂ = burning, paramagnetic; rockets = liquid O₂, N₂O₄, H₂O₂; divers = O₂+He; F = most reactive; NH₃ = refrigerators, base, lighter than air; radon = unventilated rooms.
• Boyle: T constant, P∝1/V; Charles: P constant, V∝T.
• Solids = definite shape, packed, rigid; liquids = definite volume, no shape; pressure cooker = ↑ boiling point; capillary = wick rise, blotting paper; boiling <100°C at altitude (low pressure).
• 1 atm = 760 torr = 1013.25 mbar ≈ 17.7 psi; SI = pascal; pressure ↓ up mountains.
• Water = compound (O+H); universal solvent; pH 7; sp. gravity 1; drops spherical (surface tension); freeze 0°C / 32°F; max density at 4°C; D₂O = reactor moderator (fp 3.82°C); soft = lather, hard = no lather.
• 0°F = −18°C; body temp in Fahrenheit; mercury thermometer for boiling point; know the conversion formulas.
• Filtration = filter paper, sand from water; distillation = salt+water, purifies contaminated water.
• Ore = کچی دھات; radium ← pitchblende; ores carry O and S.
• NaNO₃ = chile saltpetre (from HNO₃); soda water + CO₂; Na₂CO₃/NaHCO₃; limestone = whitewash; lime water + CO₂ → calcium bicarbonate (cloudy disappears).
• Sea salinity = NaCl per 1 kg; top sea-water elements = Na, Cl.
• Acids = sour, blue→red, common element H; HCl/nitric/sulfuric; neutralized by base; bases = bitter, slippery, red→blue, OH group; soap = base; Jabir ibn Hayyan = discoverer of sulfuric + nitric acids (bank).
• H₂SO₄ → batteries; HNO₃ → fertilizers, explosives, paints, drugs; Ca(OH)₂ → bleaching powder, water softening; milk of magnesia → stomach acidity.
• pH 0–14, 7 neutral, alkali ↑ pH; salt = ionic, acid+base → salt+water (neutralization); water = amphoteric; egg sinks pure, floats salty; CaF₂ = toothpaste, KNO₃ = fertilizer, AgNO₃ = mirrors.
• Cathode supplies electrons (metals deposit there); CuSO₄ solution = acidic; Ni–Cd = rechargeable electrodes; galvanizing = zinc coating, hot-dip method; redox = oxidation+reduction together.
• Oxidation = +O/−H; rusting & Cl₂ bleaching = oxidation; reduction = reverse; heat unit = joule; blue flame hotter; boiling egg = chemical change; binding energy = break nucleus.
• Alkanes = saturated, single σ; alkenes/alkynes = unsaturated; CH₄ = natural gas, 1:4, gobar gas.
• Coal = C,H,O (+N,S) complex mixture, top industrial fuel; wood→coal = carbonization; C-chains = catenation; coke = 1300°C, no air; peat/lignite/bituminous/anthracite 90%.
• Refining 1st = fractional distillation; LPG = butane+propane; octane no. = gasoline quality; crude → 400°C; Wöhler 1828 urea, first organic, myth broken.
• Polymerization = small→large molecule; PVC = polyvinyl chloride; nylon non-biodegradable; rayon = artificial silk; ethanol = spirit lamps, perfumes, antifreeze; TEL = anti-knock; ethene = fruit ripening; benzene C₆H₆; Ni = oil→ghee; combustion = burning; asbestos = fire resistant; hydrogenation = +H₂.
• Cement: limestone → CaCO₃, most CaO; paper recycled 5×, poplar; soap = triglyceride + NaOH/KOH; bleaching powder loses power (→ CaCl₂ + Ca(ClO₃)₂).
• Env. chemistry = pollutants; smog = visibility↓, eyes, disease, UV block; acid rain = H₂SO₄+HNO₃, soil pollution; ozone = O₃ allotrope, CFCs deplete; groundwater = worst waste effect; rain = purest water; greenhouse = long-wave absorb, CO₂+CH₄, warming = CO₂; climate = T + precipitation; cyclones = low winds; clouds = droplets; weathering = rock decay.
• Corrosion = general, rusting = iron’s corrosion; needs moist air; iron gains weight; oxalic acid removes rust stains.

10. Most-asked facts (from our verified past-paper banks)

• Elements, atoms & periodic table — 48 questions: most abundant element asked four ways — universe = hydrogen, crust = oxygen, atmosphere = nitrogen, human body = oxygen (65%); radioactivity discovered by Becquerel (asked three ways, one key spelled “Bacquerel”); gamma rays discovered by Villard; radioactivity measured by the Geiger counter; most reactive halogen = fluorine; symbol of potassium = K; gallium = Ga; element with atomic number 92 = uranium; inert gas in a bulb = argon; diamond = a form of carbon; element named after Cyprus = copper; first element transmuted by accelerators = lithium (bank answer); element in haemoglobin whose deficiency causes anaemia = iron; element used in beauty parlours for hair setting = sulfur; half-life fraction after 20 years at a 5-year half-life (the banks’ half-life calculation type).
• Metals, non-metals & alloys — 46 questions: best conductor of electricity = silver (asked five ways); metal liquid at room temperature = mercury (asked twice, including “which metal melts at room temperature”); most malleable metal = gold; first metal discovered by man = gold (asked twice); brass = copper + zinc; bronze = copper + tin; German silver = copper + nickel (asked twice); solder materials; ferrosilicon = iron + silicon; mixture of two metals = alloy (asked twice); most abundantly found metal = aluminium; second = iron; hardest metal = tungsten (bank answer); non-metal liquid = bromine; non-metal not a poor conductor = graphite (the exception question); rusting of iron as an example of corrosion; galvanizing metal = zinc; stainless steel’s chromium range (10–12%); element common to glass, cement, china clay and quartz = silicon (asked twice); the Section 4 mineral-uses table collects the mineral family (feldspar, bauxite→aluminium, hematite→iron, galena→lead, dolomite→magnesium, chromite→chromium/stainless steel, graphite, gypsum, fluorite, apatite, kaolin, asbestos, mica, quartz, gemstones — 56 unique stems across 32 bank files, 🔁⭐).
• Organic, industrial & common chemicals — 41 questions: coal deposits and resources in Pakistan dominate — largest resource, biggest deposits, Thar’s 185-billion-tonne estimate, major producing province, thermal-power and brick-kiln shares, number of coal-fired thermal stations; natural gas — formula CH₄, found in Pakistan, discovered 1952, largest producer country, largest producing province, biggest petroleum consumer sector; LPG = butane + propane (asked twice, as mixture and as abbreviation); combustion = other name of burning (asked twice); soap made by saponification; what soap is chemically; cement’s largest-quantity material; purest water from rain (asked twice); fire extinguisher for petroleum fire; 34% nitrogen fertilizer company; annual limestone production.
• Gases, water & states of matter — 34 questions: carbon monoxide’s affinity for blood (haemoglobin); gas affecting the ozone layer (CFCs); primary greenhouse-gas component (CO₂); 1987 ozone treaty (Montreal Protocol); ozone layer’s height (30 miles / 50 km, stratosphere), its UV protection, and what it prevents from reaching Earth; laughing gas = N₂O (asked twice, as name and as chemical name); evaporation causes cooling (asked twice); freezing point of water (0°C and 32°F); capillary action; surface tension falling as water temperature rises; largest CO₂ emitter; CO₂ in inhaled air; planet with 95% CO₂ (Venus); first molecule discovered in space (hydroxyl, OH); polymerisation as the union of molecules (counted here by first-match — it belongs to Section 6’s polymer block).
• Acids, bases, salts & pH — 23 questions: acid used in a car battery (sulfuric acid); table salt scientifically (sodium chloride); sulfuric + nitric acids discovered by Jabir ibn Hayyan (asked twice); alkali identification; soda water carbonated by CO₂; acid neutralized by a base/alkali (asked twice); richest source of ascorbic acid (vitamin C — Chapter 5’s vitamin block, counted here by its acid name); most common salt in seawater; salt in sweat (common mineral salt); salt raising heart-attack risk in blood; salt removed from water by distillation; heavy chemicals from common salt; biggest rock-salt deposits in Pakistan and their annual production; salt-water lake in Balochistan.
• Taught from the lecture, no direct site-bank question-text match in this run’s count: the full mixture/compound/molecule definitions as a set, the 2n² shell table and Hund’s rule as a set, the chalcogen group name, the Paschen/infrared and Crookes/cyclotron rows, the crust/ocean percentage tables as sets, the liquid-sodium coolant and mica/zirconium rows, the phosphorus-bronze spring use, the Boyle/Charles statements as laws, the thermometry conversion formulas, the chile-saltpetre and lime-water sequences, and the full environmental rows (smog harms, groundwater as worst waste effect) — the IBES Everyday Science capsule bank behind the chapter covers the chemistry rows. The practice set is filtered by tags at serve time.

11. Traps & confusions

• Four “most abundant” answers, not one: universe = hydrogen, crust = oxygen, atmosphere = nitrogen, human body = oxygen (65%). A question that says “most abundant element” without a place is usually asking the universe (hydrogen) — read the place word before choosing.
• Mixture vs compound: mixture = no fixed ratio, properties retained; compound = fixed ratio by mass, properties change. Ice cream (homogeneous mixture) vs H₂O (compound) is the pair to lock.
• Mendeleev vs modern: Mendeleev arranged by atomic mass (1869, 63 elements); the modern law arranges by atomic number. Papers swap the two bases deliberately.
• Fluorine, two superlatives: fluorine is both the most reactive halogen and the most reactive element in the lecture — astatine is the least reactive halogen. Do not let “most reactive” drift to chlorine.
• Acid/base litmus, reversed: acid turns blue → red; base turns red → blue. The colour named first is the starting litmus, not the result.
• Brass vs bronze vs German silver vs solder: brass = Cu+Zn, bronze = Cu+Sn, German silver = Cu+Ni(+Zn), solder = Sn+Pb. Zinc and tin are the two letters that separate brass from bronze — name the second metal before choosing.
• Steel vs stainless steel: plain steel = iron + carbon; stainless steel = iron + 10–12% chromium. A question that names only “steel” wants carbon, not chromium.
• Ore-name traps: chalcopyrite → copper, galena → lead, zinc blende/sphalerite → zinc, bauxite → aluminium, hematite → iron. The ore’s first syllable rarely helps — learn the pair, not the word shape. Cyanide process is a method for gold, not an ore, and open-cast is a mining method, not a mineral.
• Two liquid exceptions, opposite classes: mercury = liquid metal, bromine = liquid non-metal. “Liquid at room temperature” without a class word is ambiguous — the class word in the question picks the answer.
• Graphite breaks the non-metal rule: non-metals are poor conductors — except graphite, which conducts. “Which non-metal is not a poor conductor → graphite” is the banks’ exception question.
• CO vs CO₂, one oxygen apart: CO = poisonous (exhaust, closed-room heater, binds haemoglobin); CO₂ = fire extinguisher, greenhouse gas, soft drinks. Count the oxygens.
• Silver vs copper: silver is the best conductor; copper is the wiring metal because it is cheaper. “Best” and “used for wiring” are different questions with different answers.
• Gold, two firsts: gold is both the first metal discovered by man and the most malleable metal — same metal, two questions.
• Silicon’s double role (Chapter 6 trap, repeated): silicon is the semiconductor material and the solar-cell / solar-energy-conversion element — so “which is not a conductor → silicon” and “element required for solar energy conversion → silicon” are both right.
• Hard vs soft water: soft water lathers, hard water does not — the soap test, not the taste test.
• Lime water, two stages: CO₂ first makes lime water cloudy white (calcium carbonate), then on long passing the cloudiness disappears (soluble calcium bicarbonate). “Cloudy” and “clear again” are different stages of the same experiment.
• Heavy water vs water: ordinary water freezes at 0°C; heavy water D₂O freezes at 3.82°C and moderates reactors. The banks ask both freezing points.
• Coal ladder, ascending: peat 60% → lignite 70% → bituminous 80% → anthracite 90%. The percentages rise with quality — if you remember 90% you have anthracite, the best.
• Corrosion vs rusting: corrosion is the general term (slow eating away by the medium); rusting is iron’s corrosion, needing moist air, and iron gains weight as it rusts.
• Oxidation vs reduction: oxidation = +oxygen / −hydrogen; reduction = the reverse. Rusting and chlorine bleaching are both oxidation.
• Urea, two ureas: Wöhler’s 1828 laboratory urea (first organic compound) vs the body’s urea (made in the liver, Chapter 3). The year belongs to the synthesis, not to the body.
• “Base” questions that are not chemistry: the raw count caught dozens of maths “base of a cylinder/cone/tower” questions and military “air base” questions on the word “base” — none is counted in the 192. In chemistry, “base” means the bitter, slippery, OH-group substance unless the question says otherwise.
• “Compound” questions that are not chemistry: compound-interest, compound-wall and “own compound” questions matched the word “compound” and were removed. Chemistry compounds are fixed-ratio chemical combinations.
• Ozone year not taught: the lecture’s “depletion first seen 1990” line is omitted from this chapter — the banks test the 1987 treaty (Montreal Protocol) and the CFC cause, not a 1990 first-seen year, and standard references date the ozone hole’s discovery to 1985. The treaty year is the safe, bank-verified date.
• High pressure and storms: the lecture’s “high pressure indicates storms” line is omitted — the standard, bank-consistent fact is that cyclones are low-pressure systems; high pressure brings settled weather.

12. Memory tricks (lectures first, then clean professional hooks)

• “Brittle” is the MCQ word: solid non-metals break on pressure — if the option says “brittle”, it is describing a non-metal, not a metal.
• Shells 2–8–18–32: each shell doubles roughly (2, 8, 18, 32) — 2n² with n = 1, 2, 3, 4. Learn the doubling, not four separate numbers.
• Mendeleev 1869, 63 elements: 69 in the year hides 63 in the count — 1869 and 63 elements, both ending in the sixties’ neighbourhood; the year is 1869, the count 63.
• Brass–Zinc, Bronze–Tin: Brass ends in -ss like Zinc’s sharp sound is a stretch — cleaner: Brass = Zinc (both are the “second metal” you add to copper for everyday objects), Bronze = Tin (the older alloy — bronze age before brass). Age order: bronze (tin) first in history, brass (zinc) later.
• CO kills, CO₂ extinguishes: one oxygen = poison, two oxygens = extinguisher. Count the O’s.
• pH 7 in the middle: below 7 acid, above 7 alkali — 7 is neutral, the hinge. Alkali added to acid pushes the number up toward and past 7.
• Coal ladder 60–70–80–90: tens rising with quality — peat, lignite, bituminous, anthracite. Four types, four tens, in order.
• Alkane 1, alkene 2, alkyne 3: single, double, triple bonds in alphabetical order of the names’ endings — -ane 1, -ene 2, -yne 3.
• LPG = Butane + Propane: Butane and Propane — LPG’s two gases in alphabetical order, B then P.
• Mercury metal, bromine non-metal: the two room-temperature liquids — Mercury is a Metal, Bromine is the Brittle-class (non-metal) liquid. First letters match the class.
• Silver conducts, silicon semiconducts (Chapter 6 hook, repeated): the two S-materials — silver is the best conductor, silicon the semiconductor and the solar cell. Same letter, opposite jobs.
• Blue hotter than red: flame colour runs with temperature the same way stars do — blue is hotter than red, in a flame and in the sky.
• Galvanizing = zinc coat: Galvanizing puts a Zinc skin on steel — the coat is the protection, and hot-dip is the common method.
• Saponification = soap from fat + base: triglyceride + NaOH/KOH → soap. Fat plus base, literally the recipe in the name’s first syllable (sap- = soap).
• Wöhler 1828: urea, the first organic compound made in a lab — 1828 broke the “only nature makes organics” myth. Remember 28 as the year the myth died.
• Chalco-Copper, Blende-Zinc: Chalcopyrite carries Copper, Blende carries Zinc — and steel’s C is Carbon, the non-metal that breaks the all-metal alloy rule.

13. Visuals (site build specs)

• DIAGRAM — The periodic-table families: IA alkali, IIA alkaline earth, VIA chalcogens, VIIA halogens, 0/8A noble gases as a colour-banded group strip with fluorine (most reactive) and astatine (least reactive) called out — placed in Section 2.
• INFOGRAPHIC — The alloy table: German silver, brass, bronze, solder, ferrosilicon, phosphorus bronze and stainless steel as a composition grid (copper base vs iron base), with the brass/bronze zinc–tin split highlighted — placed in Section 4.
• INFOGRAPHIC — Ores and extraction: chalcopyrite→copper, zinc blende/sphalerite→zinc, bauxite→aluminium, hematite→iron, galena→lead as an ore→metal grid, with cyanide process (gold) and open-cast mining as method rows beside it — placed in Section 4.
• DIAGRAM — The acid–base scale: pH 0–14 strip with 7 marked neutral, litmus colours at each end (blue→red for acid, red→blue for base), and the named salts (Na₂CO₃, NaHCO₃, Ca(OH)₂, milk of magnesia) placed on it — placed in Section 3.
• INFOGRAPHIC — The coal ladder: peat 60% → lignite 70% → bituminous 80% → anthracite 90% as a rising bar chart with coke (1300°C, no air) beside it — placed in Section 6.
• DIAGRAM — CO vs CO₂: one oxygen (poisonous, exhaust, haemoglobin) beside two oxygens (extinguisher, greenhouse, soft drinks) as a paired panel — placed in Section 5.
• TIMELINE/DIAGRAM — Water’s numbers: freezing 0°C / 32°F, maximum density 4°C, heavy water 3.82°C, pressure 760 torr / 1013.25 mbar, as a single revision strip — placed in Section 5.

14. Practice this topic

• Practice set: 192 verified past-paper questions in the PPSC + FPSC banks are tagged to this topic’s sub-topics (elements, atoms & periodic table 48; acids, bases, salts & pH 23; metals, non-metals & alloys 46; gases, water & states of matter 34; organic, industrial & common chemicals 41) — the site serves them as this chapter’s practice set, with the IBES Everyday Science capsule questions behind them. Note for the build: the practice set is filtered by the topic’s subject+topic tags at serve time, so the silver-conductor question serves both this chapter’s metals set and Chapter 6’s electricity set by design, the silicon question serves both this chapter’s metalloid set and Chapter 6’s semiconductor set, and Pakistan’s coal/natural-gas questions serve both this chapter’s common-chemicals set and Chapter PS-13’s minerals set. The polymerisation question is counted in the gases/water bucket by first-match and serves from Section 6’s polymer block.
• Book mode: ← Previous: Physics in Daily Life · Next: Inventions, Discoveries & Instruments (Everyday Science) →

Goldmine Notes · Everyday Science · Chapter 7 · Sources: EDS Lecture 10 — Chemistry by Muhammad Adnan (detailed notes, rechecked) for the lecture-taught definitions, formulas, values and uses; verified PPSC/FPSC past-paper banks (192 topic questions, script-counted, hidden_files/goldmine-notes-count-eds07.py); IBES Everyday Science capsule bank behind the chapter; bank-only facts flagged in the chapter (Becquerel/Villard, tungsten hardest metal, argon in bulbs, oxygen 65% of the human body, Jabir ibn Hayyan, Montreal Protocol 1987, Venus 95% CO₂, hydroxyl first space molecule). Coverage-audit fold-in Section 4 (2026-11-03, PMS Screening 2026 Physical Science mock, 100 items): chalcopyrite, zinc blende/sphalerite, cyanide process, open-cast mining, plain steel, glass from sand, LPG expansion — bank evidence script hidden_files/goldmine-notes-count-eds07-physmock.py, no mark claimed. Standard answers only.