Physics Fundamentals — Mechanics, Heat, Electricity

Why This Chapter Matters

Chemistry supplies a steady four to six questions in SSC CGL Tier-1, and its biggest advantage over history or polity is that it rewards logic. Periodic table trends, bonding patterns, and acid-base behaviour all follow rules; once you understand the rule, you can answer questions about elements you have never specifically studied. This chapter builds that rule-based understanding rather than asking you to memorise 118 disconnected facts.

The single biggest mistake aspirants make is treating the periodic table as a list to be crammed top to bottom instead of a map with directions. Properties change predictably as you move across a period or down a group, and once that direction is fixed in your head, half the "which element has higher X" questions answer themselves. The second common trap is confusing everyday chemical names (baking soda, washing soda, quicklime, bleaching powder) with each other, since exams love testing exactly this kind of practical, kitchen-and-shop chemistry. This chapter walks through both, building from the atom outward to the compounds you actually encounter.

1. Atomic Structure: The Building Blocks

Every atom is built from three particles: protons (positive charge, in the nucleus), neutrons (no charge, in the nucleus), and electrons (negative charge, orbiting the nucleus in shells).

Particle	Charge	Relative Mass	Location	Discovered by
Proton	+1	1	Nucleus	Ernest Rutherford, 1919
Neutron	0	1	Nucleus	James Chadwick, 1932
Electron	-1	~1/1836	Shells around nucleus	J.J. Thomson, 1897

The atomic number (Z) equals the number of protons, and it defines which element an atom is; no two elements share the same atomic number. The mass number (A) equals protons plus neutrons combined. Atoms of the same element with different numbers of neutrons are called isotopes; they behave almost identically chemically but differ in mass. Carbon-12 and carbon-14 are both carbon (6 protons each), but carbon-14 carries two extra neutrons, making it useful for radioactive dating.

Electrons occupy shells labelled K, L, M, N, going outward from the nucleus, and the maximum electrons a shell can hold follows the rule 2n², where n is the shell number: K (n=1) holds up to 2, L (n=2) holds up to 8, M (n=3) holds up to 18.

Memory hook: Picture the nucleus as a locked treasure room (protons and neutrons packed tight inside) with electrons as guards patrolling assigned floors (shells) around it — the closer floors hold fewer guards, the outer floors hold more, and it's always the outermost floor's guards (valence electrons) who deal with visitors from outside, meaning they decide how the atom reacts.

The electrons in the outermost shell, called valence electrons, determine an element's chemical behaviour. This single idea explains most of the periodic table's patterns, so hold onto it as you read the next section.

Exam trap: Do not confuse atomic number with mass number. A question stating "an atom has 11 protons and 12 neutrons" is describing sodium (Z=11) with a mass number of 23, not an atom with atomic number 23.

2. The Periodic Table and Its Trends

Dmitri Mendeleev arranged elements in 1869 by increasing atomic mass, grouping elements with similar properties into columns, and famously left gaps for undiscovered elements, correctly predicting properties they would later be found to have. The modern periodic table, refined by Henry Moseley, arranges elements by increasing atomic number, not atomic mass, fixing a handful of anomalies in Mendeleev's original ordering.

The table has 18 vertical groups and 7 horizontal periods. Elements in the same group share the same number of valence electrons and so behave similarly; elements in the same period have the same number of shells but different numbers of valence electrons.

Reading the Table Like a Map

Think of the periodic table as a city grid where two directions carry meaning:

• Moving left to right across a period: atomic size decreases (more protons pull electrons in tighter), and elements become progressively less metallic and more non-metallic.
• Moving top to bottom down a group: atomic size increases (more shells added), and elements become progressively more metallic (except among noble gases, which stay largely unreactive throughout).

This single map explains most trend-based questions:

Trend	Left to Right (across period)	Top to Bottom (down group)
Atomic size	Decreases	Increases
Metallic character	Decreases	Increases
Ionisation energy	Increases	Decreases
Electronegativity	Increases	Decreases
Reactivity of metals	Decreases	Increases
Reactivity of non-metals	Increases	Decreases

Ionisation energy is the energy required to remove an electron from an atom. It rises across a period because the nucleus holds electrons more tightly as protons increase, and it falls down a group because outer electrons sit farther from the nucleus and are more loosely held, shielded by inner shells.

Electronegativity is an atom's tendency to attract shared electrons in a bond. Fluorine is the most electronegative element on the entire table, sitting at the top-right corner where both trends (rightward and upward) push electronegativity to its maximum.

Memory hook: "Top-right corner is greedy" — elements near fluorine and oxygen sit at the intersection of both high-electronegativity trends, making them the most eager electron-grabbers on the table.

Metals, Non-Metals, and Metalloids

Metals occupy the left and centre of the table (roughly 78% of all elements). They are shiny, malleable (can be hammered into sheets), ductile (can be drawn into wires), good conductors of heat and electricity, and tend to lose electrons in reactions to form positive ions (cations).

Non-metals sit on the right side of the table. They are typically dull, brittle in solid form, poor conductors (with the notable exception of graphite, a form of carbon that conducts electricity), and tend to gain electrons to form negative ions (anions).

Metalloids (like silicon, germanium, arsenic) sit along the zigzag staircase line separating metals from non-metals, showing properties of both, most famously used as semiconductors in electronics.

Exam trap: Mercury is the only metal that is liquid at room temperature; bromine is the only non-metal that is liquid at room temperature. These two facts get swapped constantly in MCQ options, so anchor them separately: Mercury (metal) fills old-style thermometers; Bromine (non-metal) is a reddish-brown liquid used in some flame retardants and dyes.

3. Chemical Bonding

Atoms bond to achieve a stable outer shell, generally aiming for eight valence electrons (the octet rule), mimicking the stable configuration of noble gases. Two main types of bonding matter for exams.

Ionic Bonding

Formed when one atom transfers electrons to another, creating oppositely charged ions that attract each other electrostatically. This typically happens between a metal (which loses electrons easily) and a non-metal (which gains electrons easily). Sodium chloride (table salt) is the textbook example: sodium loses one electron to become Na⁺, chlorine gains that electron to become Cl⁻, and the two ions bond through electrostatic attraction. Ionic compounds tend to have high melting points, dissolve in water, and conduct electricity when molten or dissolved (because the ions become free to move and carry charge).

Covalent Bonding

Formed when two atoms share electrons rather than transferring them, typically between two non-metals. Water (H₂O) shares electrons between oxygen and two hydrogen atoms; oxygen gas (O₂) shares electrons between two oxygen atoms via a double bond. Covalent compounds generally have lower melting points than ionic compounds and do not conduct electricity in any state, since there are no free-moving charged particles.

Memory hook: Ionic bonding is a transaction — one atom "gives," the other "takes," like a shopkeeper handing over goods for money (a complete transfer). Covalent bonding is a partnership — both atoms "share" custody of the electrons, like two families sharing a common courtyard wall between adjoining houses.

Exam trap: Students sometimes think metals only form ionic bonds. Two metal atoms bonding to each other (as in a block of iron or copper) actually forms metallic bonding, a third distinct type where electrons move freely through a "sea of electrons" shared by all atoms in the metal — this freely moving electron sea is exactly what makes metals such good electrical conductors.

4. Acids, Bases, and Salts

An acid is a substance that releases H⁺ ions in water, tastes sour, turns blue litmus paper red, and has a pH less than 7. A base is a substance that releases OH⁻ ions in water, tastes bitter, feels slippery, turns red litmus paper blue, and has a pH greater than 7. A substance with pH exactly 7 is neutral, pure water being the standard example.

The pH scale runs from 0 to 14. Lower numbers mean stronger acids (battery acid sits near 0-1), higher numbers mean stronger bases (drain cleaner sits near 13-14), and 7 sits exactly in the middle as neutral.

Memory hook: Picture the pH scale as a seesaw with water (pH 7) balanced exactly at the centre pivot — everything sliding toward 0 gets more acidic, everything sliding toward 14 gets more basic, and the further from the centre, the more extreme (and more corrosive) the substance.

Litmus paper is the classic acid-base indicator, made from lichen extract: blue litmus turns red in acid; red litmus turns blue in base. Other natural indicators include red cabbage extract and turmeric (which turns from yellow to red in basic solutions).

Neutralisation is the reaction between an acid and a base, producing a salt and water. This is why antacid tablets (mild bases) relieve acidity: they neutralise excess hydrochloric acid in the stomach. Farmers use lime (a base) to neutralise excess acidity in soil for the same underlying reason.

Common Acids and Bases in Daily Life

Substance	Chemical Name	Everyday Source
Acetic acid	CH₃COOH	Vinegar
Citric acid	C₆H₈O₇	Lemon, citrus fruits
Lactic acid	C₃H₆O₃	Curd, sour milk
Ascorbic acid	C₆H₈O₆	Vitamin C, citrus fruits
Hydrochloric acid	HCl	Gastric (stomach) juice
Carbonic acid	H₂CO₃	Soda water, carbonated drinks
Sodium hydroxide	NaOH	Caustic soda, soap-making
Calcium hydroxide	Ca(OH)₂	Slaked lime, whitewash
Ammonium hydroxide	NH₄OH	Household ammonia cleaners

Common Salts and Their Everyday Names

This is one of the most heavily tested corners of school chemistry because the "kitchen name" and the "chemical name" rarely match.

Everyday Name	Chemical Name	Chemical Formula	Common Use
Baking soda	Sodium bicarbonate	NaHCO₃	Baking, mild antacid
Washing soda	Sodium carbonate	Na₂CO₃·10H₂O	Cleaning, glass-making
Common salt	Sodium chloride	NaCl	Cooking, food preservation
Quicklime	Calcium oxide	CaO	Cement, whitewashing base
Slaked lime	Calcium hydroxide	Ca(OH)₂	Whitewash, soil treatment
Bleaching powder	Calcium oxychloride	CaOCl₂	Disinfecting water, bleaching
Plaster of Paris	Calcium sulphate hemihydrate	CaSO₄·½H₂O	Casts, sculpture moulds
Gypsum	Calcium sulphate dihydrate	CaSO₄·2H₂O	Cement, blackboard chalk
Epsom salt	Magnesium sulphate	MgSO₄·7H₂O	Bath salts, laxative
Blue vitriol	Copper sulphate	CuSO₄·5H₂O	Fungicide, electroplating

Exam trap: Baking soda and washing soda are constantly confused because both are sodium-based and both are "soda." Fix it by function: baking soda (NaHCO₃) is mild enough to eat, used in cooking and as an antacid; washing soda (Na₂CO₃) is a stronger cleaning agent, never consumed, used in glass manufacturing and detergents. If a question mentions eating, medicine, or antacid, it means baking soda; if it mentions cleaning or glass, it means washing soda.

Water of crystallisation is the fixed number of water molecules chemically bound within a crystal's structure, shown by the dot notation (like CuSO₄·5H₂O, copper sulphate with five water molecules per formula unit). Heating removes this water and often changes the crystal's colour, which is how blue copper sulphate crystals turn white powder on strong heating.

5. Metals and Non-Metals in Depth

Reactivity Series

The reactivity series (activity series) ranks metals by how readily they lose electrons and react. A commonly taught order, from most to least reactive: Potassium, Sodium, Calcium, Magnesium, Aluminium, Zinc, Iron, Lead, Hydrogen, Copper, Silver, Gold.

Memory hook: "Please Send Cars, Monkeys Are Zooming, Impatiently Leaving; Happy Customers Save Gold" — the first letters trace Potassium-Sodium-Calcium-Magnesium-Aluminium-Zinc-Iron-Lead-Hydrogen-Copper-Silver-Gold in descending order of reactivity.

Metals above hydrogen in this series can displace hydrogen from dilute acids (zinc reacting with dilute sulphuric acid releases hydrogen gas); metals below hydrogen, like copper, silver, and gold, cannot. This is also why gold and silver are found in nature in their free, uncombined state — they are so unreactive they rarely form compounds with other elements in the ground, unlike iron, which almost always occurs combined as an ore (like iron oxide) and must be extracted through a chemical process.

Extraction and Corrosion

Extracting a metal from its ore generally requires more energy the higher that metal sits on the reactivity series, because a more reactive metal binds to its ore more tightly and resists being separated. This is why gold, at the bottom, needs almost no chemical extraction (often found as nuggets), while aluminium, high on the series, requires an energy-intensive electrolytic process (the Hall-Héroult process) to extract from bauxite ore.

Corrosion is the gradual destruction of a metal by chemical reaction with its environment, most familiar as rusting, the reaction of iron with oxygen and moisture to form hydrated iron oxide (Fe₂O₃·xH₂O). Rusting needs both air and water together; iron kept perfectly dry, or fully submerged with no dissolved oxygen, rusts far more slowly. Preventing rust (painting, galvanising with a zinc coating, alloying into stainless steel) is a direct application of this chemistry, and a frequent exam question.

Memory hook: Rust needs a "wet handshake with air" — remove either the water or the oxygen, and the handshake, and the rust, cannot happen.

Alloys

An alloy is a mixture of a metal with one or more other elements (often another metal, sometimes a non-metal like carbon), designed to improve properties like strength, resistance to corrosion, or hardness.

Alloy	Composition	Key Use
Stainless steel	Iron, chromium, nickel	Cutlery, surgical instruments
Brass	Copper, zinc	Musical instruments, fittings
Bronze	Copper, tin	Statues, medals
Solder	Tin, lead	Joining electrical wires
Duralumin	Aluminium, copper, magnesium	Aircraft bodies

6. Carbon Compounds and Organic Chemistry Basics

Organic chemistry is the study of carbon compounds, a field vast enough to deserve its own branch because of one unusual property: carbon can bond to itself repeatedly, forming long chains, branches, and rings, a property called catenation. This single ability is why carbon compounds outnumber all other elements' compounds combined, forming the chemical basis of every living organism as well as fuels, plastics, and medicines.

Carbon has 4 valence electrons, so it forms 4 covalent bonds with other atoms, most commonly hydrogen, oxygen, nitrogen, and other carbon atoms.

Hydrocarbons

The simplest organic compounds contain only carbon and hydrogen, called hydrocarbons, split into two families:

• Saturated hydrocarbons (alkanes): contain only single bonds between carbon atoms (methane CH₄, ethane C₂H₆, propane C₃H₈).
• Unsaturated hydrocarbons (alkenes and alkynes): contain at least one double bond (alkenes, like ethylene C₂H₄) or triple bond (alkynes, like acetylene C₂H₂) between carbon atoms.

Memory hook: "Saturated" means "full up," like a saturated sponge that cannot absorb more water — a saturated hydrocarbon's carbon atoms are similarly "full," bonded to the maximum possible number of hydrogen atoms, leaving no room for a double or triple bond.

Functional Groups

A functional group is a specific arrangement of atoms attached to a carbon chain that determines a compound's chemical behaviour, regardless of how long the rest of the chain is.

Functional Group	Suffix	Example
Alcohol (-OH)	-ol	Ethanol (C₂H₅OH)
Aldehyde (-CHO)	-al	Ethanal (CH₃CHO)
Ketone (-CO-)	-one	Propanone (acetone)
Carboxylic acid (-COOH)	-oic acid	Ethanoic acid (acetic acid)

Ethanol (C₂H₅OH), ordinary drinking alcohol, is also used as a fuel additive and industrial solvent. Ethanoic acid (acetic acid, CH₃COOH), in its roughly 5-8% dilute form, is what you know as vinegar.

Exam trap: Methane and methanol sound alike but differ completely: methane (CH₄) is the simplest hydrocarbon, the main component of natural gas and a potent greenhouse gas released by cattle and landfills; methanol (CH₃OH) is a toxic alcohol, used as an industrial solvent, entirely unsafe to drink (unlike ethanol) and a known cause of poisoning when adulterated liquor contains it.

Polymers

A polymer is a large molecule built from many repeating smaller units called monomers, linked in long chains. Natural polymers include cellulose (in plant cell walls), starch, and proteins; synthetic polymers include plastics like polyethylene (from the monomer ethylene) and PVC (polyvinyl chloride). This chapter's coverage stops at recognising the term, since detailed polymer chemistry rarely appears at SSC level beyond identifying common plastics and their monomers.

7. Everyday Chemistry

Soaps and Detergents

Soap is made through saponification: heating natural fats or oils with a strong base (sodium hydroxide for hard bar soap, potassium hydroxide for liquid soap), which breaks the fat into soap molecules and glycerol as a byproduct. A soap molecule has two distinct ends: a hydrophilic (water-loving) head and a hydrophobic (water-repelling, oil-loving) tail. When you wash greasy hands, the tail end buries into the grease while the head end stays in the surrounding water, and together these clusters (called micelles) lift the grease away and let water rinse it off.

Memory hook: A soap molecule behaves like a tiny two-sided tool: one end grabs the dirt (oil-loving tail), the other end lets water carry it away (water-loving head), working like a person holding a rope with one hand on a boat and the other on the dock, pulling the two together.

Exam trap: Soaps do not work well in hard water (water containing dissolved calcium and magnesium salts), because these ions react with soap to form an insoluble scum instead of a proper lather, wasting soap and leaving residue. Synthetic detergents, chemically different from soap, are specifically designed to avoid this problem and work equally well in hard or soft water, which is why liquid detergents remain effective for laundry in hard-water regions while ordinary soap performs poorly there.

Fuels

A fuel is a substance burned to release energy, usually through combustion, a reaction with oxygen that releases heat and light. Calorific value, the amount of heat released per unit mass of fuel burned, measures how efficient a fuel is; hydrogen has an exceptionally high calorific value, one reason it is explored as a clean fuel, though storage and production challenges limit widespread use so far.

Fossil fuels (coal, petroleum, natural gas) formed over millions of years from the decomposed remains of ancient plants and organisms under heat and pressure, which is why they are called non-renewable: they take far longer to form than humanity uses them. Petroleum refining separates crude oil into fractions like LPG, petrol, diesel, and kerosene based on differing boiling points, through a process called fractional distillation.

Complete combustion (sufficient oxygen supply) of a hydrocarbon fuel produces carbon dioxide and water, releasing more energy; incomplete combustion (insufficient oxygen) produces carbon monoxide, a poisonous gas, along with soot, releasing comparatively less energy. This is exactly why a well-ventilated kitchen stove burns with a clean blue flame, while a poorly ventilated room with a gas heater can pose a carbon monoxide poisoning risk.

Quick Revision — One-Line Facts

1. Atomic number (Z) = number of protons; mass number (A) = protons + neutrons.
2. Isotopes have the same atomic number but different mass numbers.
3. A shell's maximum electron capacity follows the rule 2n².
4. Valence electrons (outermost shell) determine chemical reactivity.
5. Mendeleev arranged elements by atomic mass (1869); the modern table uses atomic number (Moseley).
6. Atomic size decreases left to right across a period, increases down a group.
7. Metallic character decreases left to right, increases down a group.
8. Fluorine is the most electronegative element on the periodic table.
9. Mercury is the only metal liquid at room temperature; bromine is the only liquid non-metal.
10. Ionic bonds form by electron transfer (usually metal + non-metal); covalent bonds form by electron sharing (usually non-metal + non-metal).
11. Metallic bonding involves a "sea of electrons" shared among metal atoms.
12. Acids release H⁺ ions, pH less than 7, turn blue litmus red.
13. Bases release OH⁻ ions, pH greater than 7, turn red litmus blue.
14. Neutralisation between an acid and a base produces a salt and water.
15. Baking soda is sodium bicarbonate (NaHCO₃); washing soda is sodium carbonate (Na₂CO₃).
16. Quicklime is calcium oxide (CaO); slaked lime is calcium hydroxide (Ca(OH)₂).
17. Bleaching powder is calcium oxychloride (CaOCl₂).
18. Plaster of Paris is calcium sulphate hemihydrate, used in casts and moulds.
19. The reactivity series ranks metals from Potassium (most reactive) to Gold (least reactive).
20. Gold and silver occur naturally in free/uncombined state due to low reactivity.
21. Rusting of iron requires both oxygen and moisture together.
22. Stainless steel is an alloy of iron, chromium, and nickel.
23. Bronze is copper and tin; brass is copper and zinc.
24. Carbon's catenation (self-bonding) property explains the vast scope of organic chemistry.
25. Carbon has 4 valence electrons and forms 4 covalent bonds.
26. Alkanes are saturated hydrocarbons (single bonds only); alkenes/alkynes are unsaturated.
27. Ethanol (C₂H₅OH) is drinking alcohol; methanol (CH₃OH) is toxic industrial alcohol.
28. Vinegar is dilute acetic acid (ethanoic acid, CH₃COOH).
29. Soap is made via saponification: fat/oil + strong base + heat, yielding soap and glycerol.
30. Soaps form scum in hard water; synthetic detergents work in both hard and soft water.
31. Complete combustion of fuel produces CO₂ and water; incomplete combustion produces poisonous CO.
32. Petroleum refining uses fractional distillation, separating fractions by boiling point.

Memory Tables

Table 1: Periodic Table Trends at a Glance

Property	Left → Right (period)	Top → Bottom (group)
Atomic size	Decreases	Increases
Metallic character	Decreases	Increases
Ionisation energy	Increases	Decreases
Electronegativity	Increases	Decreases
Reactivity (metals)	Decreases	Increases
Reactivity (non-metals)	Increases	Decreases

Table 2: Common Chemical Names vs. Everyday Names

Everyday Name	Chemical Name	Formula
Baking soda	Sodium bicarbonate	NaHCO₃
Washing soda	Sodium carbonate	Na₂CO₃·10H₂O
Common salt	Sodium chloride	NaCl
Quicklime	Calcium oxide	CaO
Slaked lime	Calcium hydroxide	Ca(OH)₂
Bleaching powder	Calcium oxychloride	CaOCl₂
Plaster of Paris	Calcium sulphate hemihydrate	CaSO₄·½H₂O
Blue vitriol	Copper sulphate	CuSO₄·5H₂O
Epsom salt	Magnesium sulphate	MgSO₄·7H₂O
Vinegar (active ingredient)	Acetic/ethanoic acid	CH₃COOH

Practice MCQs

Q1. The atomic number of an element is equal to the number of: (a) Neutrons (b) Protons (c) Protons + Neutrons (d) Electrons + Neutrons

Q2. Isotopes of an element differ in: (a) Atomic number (b) Number of protons (c) Number of neutrons (d) Chemical properties entirely

Q3. Who rearranged the periodic table based on atomic number instead of atomic mass? (a) Dmitri Mendeleev (b) Henry Moseley (c) John Dalton (d) Antoine Lavoisier

Q4. As you move down a group in the periodic table, atomic size generally: (a) Increases (b) Decreases (c) Remains constant (d) First increases, then decreases

Q5. Which element is the most electronegative on the periodic table? (a) Oxygen (b) Chlorine (c) Fluorine (d) Nitrogen

Q6. Which of the following metals is liquid at room temperature? (a) Sodium (b) Mercury (c) Gold (d) Aluminium

Q7. Ionic bonds are most commonly formed between: (a) Two metals (b) Two non-metals (c) A metal and a non-metal (d) Two noble gases

Q8. A substance with pH 3 is: (a) Strongly basic (b) Neutral (c) Strongly acidic (d) Mildly basic

Q9. Baking soda is chemically known as: (a) Sodium carbonate (b) Sodium bicarbonate (c) Calcium carbonate (d) Calcium bicarbonate

Q10. Which gas is released when zinc reacts with dilute sulphuric acid? (a) Oxygen (b) Carbon dioxide (c) Hydrogen (d) Nitrogen

Q11. Rusting of iron requires the simultaneous presence of: (a) Only oxygen (b) Only water (c) Both oxygen and water (d) Neither oxygen nor water

Q12. Stainless steel is an alloy primarily composed of iron along with: (a) Tin and lead (b) Chromium and nickel (c) Copper and zinc (d) Aluminium and magnesium

Q13. The property of carbon that allows it to form long chains and rings is called: (a) Isomerism (b) Catenation (c) Valency (d) Ionisation

Q14. Which of the following is a saturated hydrocarbon? (a) Ethylene (C₂H₄) (b) Acetylene (C₂H₂) (c) Ethane (C₂H₆) (d) Benzene (C₆H₆)

Q15. Soaps are less effective in hard water because: (a) Hard water is too acidic (b) Hard water dissolves soap completely (c) Calcium and magnesium ions in hard water form insoluble scum with soap (d) Hard water contains no minerals at all

Answer Key

Q	Answer	One-line reason
1	(b) Protons	Atomic number is defined strictly as the number of protons in the nucleus.
2	(c) Number of neutrons	Isotopes share the same atomic number (protons) but differ in neutron count and mass number.
3	(b) Henry Moseley	Moseley's work established atomic number, not atomic mass, as the correct basis for the modern periodic table.
4	(a) Increases	Each new period adds a shell, so atomic size grows going down a group.
5	(c) Fluorine	Fluorine sits at the top-right corner where both electronegativity trends peak together.
6	(b) Mercury	Mercury is the only metal that stays liquid at normal room temperature, used historically in thermometers.
7	(c) A metal and a non-metal	Ionic bonds form through electron transfer, typically from an electron-losing metal to an electron-gaining non-metal.
8	(c) Strongly acidic	pH below 7 indicates acidity, and 3 is well below neutral, making it strongly acidic.
9	(b) Sodium bicarbonate	Baking soda is NaHCO₃, mild enough for cooking and as an antacid, unlike the stronger washing soda.
10	(c) Hydrogen	Zinc, being above hydrogen in the reactivity series, displaces hydrogen gas from dilute acids.
11	(c) Both oxygen and water	Rusting is a reaction of iron with both atmospheric oxygen and moisture together; removing either slows it drastically.
12	(b) Chromium and nickel	Stainless steel adds chromium and nickel to iron for corrosion resistance and shine.
13	(b) Catenation	Catenation is carbon's unique ability to bond repeatedly with itself, forming chains and rings.
14	(c) Ethane (C₂H₆)	Ethane has only single carbon-carbon bonds, making it saturated; the others contain double or aromatic bonds.
15	(c) Calcium and magnesium ions in hard water form insoluble scum with soap	This scum wastes soap and prevents proper lathering, unlike with synthetic detergents.