Sample Question Paper · 2025–26
SCIENCE
Class X · Theory · Code No. 086
General Instructions
- This question paper consists of 39 questions in 5 sections.
- Section A consists of 20 objective-type questions carrying 1 mark each.
- Section B consists of 6 questions of 2 marks each. Answers should not exceed 40 words.
- Section C consists of 7 questions of 3 marks each. Answers should not exceed 60 words.
- Section D consists of 3 questions of 5 marks each. Answers should not exceed 120 words.
- Section E consists of 3 case-based/source-based questions of 4 marks each, with sub-parts.
- There is no overall choice. However, internal choices have been provided in a few questions.
- Wherever necessary, neat, labelled diagrams should be drawn.
- Use of calculators is not permitted.
Section A
Q1–Q20 · 1 mark each · 20 marks1.
The ability of metals to be beaten into thin sheets is called: 1
2.
Which of the following metals is stored in kerosene oil? 1
3.
The chemical formula of quick lime is: 1
4.
Which gas is liberated when zinc reacts with dilute sulphuric acid? 1
5.
An element X forms an oxide X₂O₃ which is amphoteric in nature. X is most likely to be: 1
6.
Rusting of iron is an example of: 1
7.
Which of the following metals does NOT react with dilute hydrochloric acid? 1
8.
A solution turns red litmus blue. Its pH is likely to be: 1
9.
The most malleable and ductile metal is: 1
10.
Which metal is obtained by electrolytic reduction of its molten oxide/chloride? 1
11.
Galvanisation is the process of coating iron with a layer of: 1
12.
In the reaction Fe₂O₃ + 2Al → 2Fe + Al₂O₃, aluminium acts as a: 1
13.
Brass is an alloy of: 1
14.
Which of the following is a double displacement reaction? 1
15.
Which gas turns lime water milky? 1
16.
Assertion (A): Ionic compounds conduct electricity in molten state.
Reason (R): In the molten state, ions are free to move and carry charge.1
Reason (R): In the molten state, ions are free to move and carry charge.1
17.
Assertion (A): Aluminium is used to make cooking utensils despite being reactive.
Reason (R): Aluminium forms a protective oxide layer that resists further corrosion.1
Reason (R): Aluminium forms a protective oxide layer that resists further corrosion.1
18.
Which of the following correctly represents a balanced chemical equation? 1
19.
The pH of pure water at 298 K is: 1
20.
A non-metal X is a poor conductor of electricity but its allotrope Y conducts electricity. X and Y respectively could be: 1
Section B
Q21–Q26 · 2 marks each · 12 marks21.
Why is aluminium oxide classified as an amphoteric oxide? Support your answer with one chemical equation. 2
22.
What is a balanced chemical equation? Why should chemical equations be balanced? 2
23.
State two ways by which the rusting of iron can be prevented. 2
24.
Differentiate between roasting and calcination, giving one example of each. 2
25.
What happens chemically when quick lime is left exposed to air for a long time? Write the relevant equation. 2
OR
Write the chemical equation when iron reacts with steam, and name the type of reaction.
26.
Why does copper not react with dilute HCl, while zinc does? Relate your answer to the reactivity series. 2
Section C
Q27–Q33 · 3 marks each · 21 marks27.
Define corrosion. Describe the conditions necessary for iron to rust, referring to a suitable experiment that demonstrates this. 3
28.
(a) What is meant by a displacement reaction?
(b) On the basis of the reactivity series, predict and write the equation for the reaction (if any) between iron and copper sulphate solution.
(c) Name the type of this reaction. 3
(b) On the basis of the reactivity series, predict and write the equation for the reaction (if any) between iron and copper sulphate solution.
(c) Name the type of this reaction. 3
29.
Explain, with the help of a labelled diagram, how the formation of sodium chloride takes place through the transfer of electrons. 3
30.
(a) What is an alloy?
(b) Name the constituents of stainless steel and state one property that makes it useful.
(c) Why are alloys generally poorer conductors of electricity than their constituent pure metals? 3
(b) Name the constituents of stainless steel and state one property that makes it useful.
(c) Why are alloys generally poorer conductors of electricity than their constituent pure metals? 3
31.
Write balanced chemical equations for the following reactions:
(a) Aluminium reacting with steam
(b) Calcium reacting with water
(c) Zinc oxide reacting with carbon (reduction) 3
(a) Aluminium reacting with steam
(b) Calcium reacting with water
(c) Zinc oxide reacting with carbon (reduction) 3
32.
List in tabular form three physical properties in which metals differ from non-metals, and give one exception for each property. 3
OR
A man cleaned old, dull gold jewellery by dipping it in a particular liquid. The jewellery sparkled, but its weight reduced sharply. Identify the nature of the liquid used and explain the chemistry behind this observation.
33.
A compound X has a high melting point. It is soluble in water but insoluble in kerosene. Its aqueous solution conducts electricity, but X does not conduct electricity in the solid state.
(a) What type of bonding is present in X?
(b) Explain why X conducts electricity only in molten/dissolved state.
(c) Identify a likely example of X. 3
(a) What type of bonding is present in X?
(b) Explain why X conducts electricity only in molten/dissolved state.
(c) Identify a likely example of X. 3
Section D
Q34–Q36 · 5 marks each · 15 marks34.
(a) State the general principles of extraction of metals based on their position in the activity (reactivity) series. Give one example of a metal extracted from each of the three categories: highly reactive, moderately reactive, and least reactive.
(b) Why must carbonate and sulphide ores be converted to oxides before reduction? 5
(b) Why must carbonate and sulphide ores be converted to oxides before reduction? 5
OR
(a) What is the activity (reactivity) series of metals? Arrange the following in decreasing order of reactivity: Copper, Sodium, Iron, Gold, Zinc.
(b) Explain, with examples, how a more reactive metal can displace a less reactive metal from its salt solution.
(c) Name two metals which do not react with dilute acids, giving a reason.
(b) Explain, with examples, how a more reactive metal can displace a less reactive metal from its salt solution.
(c) Name two metals which do not react with dilute acids, giving a reason.
35.
(a) Differentiate between a combination reaction, a decomposition reaction, and a displacement reaction, with one balanced equation as an example for each.
(b) Identify the type of reaction in each of the following and balance them:
(i) Fe + H₂O(steam) → ___ + ___
(ii) CaCO₃ → ___ + ___
(iii) AgNO₃ + NaCl → ___ + ___ 5
(b) Identify the type of reaction in each of the following and balance them:
(i) Fe + H₂O(steam) → ___ + ___
(ii) CaCO₃ → ___ + ___
(iii) AgNO₃ + NaCl → ___ + ___ 5
36.
(a) What are ionic compounds? Describe, with an example, how ionic compounds are formed.
(b) List four general physical properties of ionic compounds.
(c) Why do ionic compounds have high melting and boiling points? 5
(b) List four general physical properties of ionic compounds.
(c) Why do ionic compounds have high melting and boiling points? 5
OR
(a) What is anodising? Why is it carried out on aluminium articles?
(b) What is galvanisation? Explain why a galvanised iron article continues to resist rusting even if the protective zinc coating gets locally scratched.
(c) Distinguish between roasting and calcination with one example each.
(b) What is galvanisation? Explain why a galvanised iron article continues to resist rusting even if the protective zinc coating gets locally scratched.
(c) Distinguish between roasting and calcination with one example each.
Section E
Q37–Q39 · Case-based · 4 marks each · 12 marks37.
Read the following passage and answer the questions that follow:
Riya performed an experiment in her school laboratory. She placed small pieces of sodium, calcium, magnesium, and copper separately in beakers of cold water. She observed that sodium reacted very violently, calcium reacted gently and started floating, magnesium showed almost no reaction with cold water, and copper showed no reaction at all. Her teacher then asked her to repeat the experiment with magnesium using hot water instead.
Riya performed an experiment in her school laboratory. She placed small pieces of sodium, calcium, magnesium, and copper separately in beakers of cold water. She observed that sodium reacted very violently, calcium reacted gently and started floating, magnesium showed almost no reaction with cold water, and copper showed no reaction at all. Her teacher then asked her to repeat the experiment with magnesium using hot water instead.
(a) Why did sodium react so violently with cold water compared to calcium? 1
(b) Why did calcium start floating on water? 1
(c) Write the balanced chemical equation for the reaction of magnesium with hot water. 1
(d) Arrange sodium, calcium, magnesium, and copper in decreasing order of reactivity based on Riya's observations. 1
(b) Why did calcium start floating on water? 1
(c) Write the balanced chemical equation for the reaction of magnesium with hot water. 1
(d) Arrange sodium, calcium, magnesium, and copper in decreasing order of reactivity based on Riya's observations. 1
38.
Read the following passage and answer the questions that follow:
In a chemistry class, the teacher demonstrated a reaction by adding dilute hydrochloric acid to a test tube containing zinc granules. Bubbles of a colourless gas were produced, which the teacher tested with a burning matchstick — the gas burned with a 'pop' sound. The teacher then explained that this gas does not support combustion of the matchstick itself, but burns on contact with a flame.
In a chemistry class, the teacher demonstrated a reaction by adding dilute hydrochloric acid to a test tube containing zinc granules. Bubbles of a colourless gas were produced, which the teacher tested with a burning matchstick — the gas burned with a 'pop' sound. The teacher then explained that this gas does not support combustion of the matchstick itself, but burns on contact with a flame.
(a) Identify the gas produced in the reaction. 1
(b) Write the balanced chemical equation for the reaction between zinc and dilute hydrochloric acid. 1
(c) Name the type of chemical reaction taking place. 1
(d) Would the same gas be produced if copper were used instead of zinc? Justify your answer. 1
(b) Write the balanced chemical equation for the reaction between zinc and dilute hydrochloric acid. 1
(c) Name the type of chemical reaction taking place. 1
(d) Would the same gas be produced if copper were used instead of zinc? Justify your answer. 1
39.
Read the following passage and answer the questions that follow:
Sodium chloride is a common ionic compound formed by the transfer of an electron from a sodium atom to a chlorine atom. The sodium atom (electronic configuration 2,8,1) loses one electron to attain a stable configuration, while the chlorine atom (electronic configuration 2,8,7) gains one electron to complete its octet. The oppositely charged ions formed are then held together by strong electrostatic forces of attraction.
Sodium chloride is a common ionic compound formed by the transfer of an electron from a sodium atom to a chlorine atom. The sodium atom (electronic configuration 2,8,1) loses one electron to attain a stable configuration, while the chlorine atom (electronic configuration 2,8,7) gains one electron to complete its octet. The oppositely charged ions formed are then held together by strong electrostatic forces of attraction.
Na (2,8,1)→ Na⁺ (2,8) + e⁻Cl (2,8,7) + e⁻→ Cl⁻ (2,8,8)
(a) Name the ions formed when sodium chloride is formed. 1
(b) Why does solid sodium chloride not conduct electricity, while its aqueous solution does? 1
(c) Why does sodium chloride have a high melting point? 1
(d) Predict whether sodium chloride would be soluble in kerosene. Give a reason. 1
(b) Why does solid sodium chloride not conduct electricity, while its aqueous solution does? 1
(c) Why does sodium chloride have a high melting point? 1
(d) Predict whether sodium chloride would be soluble in kerosene. Give a reason. 1
— End of Question Paper —
Sample Question Paper · 2025–26
SCIENCE — DETAILED ANSWER KEY
Class X · Theory · Code No. 086 · Maximum Marks 80
Section A — Answers
1 mark each1.(b) Malleability
WhyMalleability is specifically the property of being hammered/beaten into thin sheets. Ductility refers to wires, not sheets.
2.(b) Sodium
WhySodium (and potassium) react so vigorously with atmospheric oxygen and moisture that they can catch fire spontaneously; kerosene oil seals them off from air and water.
3.(c) CaO
WhyQuick lime is calcium oxide (CaO), produced by heating limestone (CaCO₃). Ca(OH)₂ is slaked lime, not quick lime.
4.(b) Hydrogen
WhyZn + H₂SO₄ → ZnSO₄ + H₂↑. Active metals react with dilute acids to liberate hydrogen gas.
5.(b) Aluminium
WhyAluminium forms Al₂O₃, a classic amphoteric oxide that reacts with both acids and bases (e.g. with HCl and with NaOH).
6.(c) Oxidation reaction
WhyRusting involves iron losing electrons to oxygen in the presence of moisture, forming hydrated iron(III) oxide — a slow oxidation process.
7.(c) Copper
WhyCopper lies below hydrogen in the reactivity series, so it cannot displace H₂ from dilute HCl. Mg, Zn, and Al are all above hydrogen.
8.(d) 10
WhyTurning red litmus blue indicates a basic/alkaline solution. Basic solutions have pH greater than 7; among the options, only 10 qualifies.
9.(c) Gold
WhyGold is the most malleable and ductile metal known — 1 gram of gold can be drawn into a wire roughly 2 km long.
10.(d) Sodium
WhySodium sits at the top of the reactivity series. It has more affinity for oxygen/chlorine than carbon does, so it must be extracted by electrolysis of its molten compound, not by carbon reduction.
11.(c) Zinc
WhyGalvanisation specifically refers to coating iron/steel with a thin protective layer of zinc to prevent rusting.
12.(b) Reducing agent
WhyAluminium reduces Fe₂O₃ to Fe by removing oxygen from it (itself getting oxidised to Al₂O₃). A substance that removes oxygen from another is a reducing agent. This is the thermit reaction.
13.(b) Copper and zinc
WhyBrass = Cu + Zn. Bronze = Cu + Sn. Solder = Pb + Sn. Stainless steel = Fe + Ni + Cr.
14.(c) Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
WhyBoth reacting compounds exchange ions to form two new compounds — the defining feature of a double displacement reaction. Option (d) is a single displacement (Zn displaces Cu).
15.(c) Carbon dioxide
WhyCO₂ reacts with calcium hydroxide (lime water) to form insoluble calcium carbonate, which causes the milky appearance: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O.
16.(a) Both A and R true, R explains A
WhyIn the molten state, the rigid ionic lattice breaks down and ions become mobile, allowing them to carry electric charge — this is precisely why molten ionic compounds conduct electricity.
17.(a) Both A and R true, R explains A
WhyThe thin, tough Al₂O₃ layer that forms naturally on aluminium's surface protects the underlying metal from further reaction, making it safe and practical for cookware despite aluminium's inherent reactivity.
18.(b) 2H₂ + O₂ → 2H₂O
WhyAtom count must match on both sides. Left: 4 H, 2 O. Right: 4 H, 2 O. Balanced. Option (a) has 2 O unaccounted for; (c) and (d) are also unbalanced.
19.(b) 7
WhyPure water is neutral, with an equal concentration of H⁺ and OH⁻ ions, giving it a pH of exactly 7 at 298 K.
20.(b) Graphite, Diamond — reversed: X = Diamond, Y = Graphite
WhyBoth are allotropes of carbon. Diamond (X) is a poor conductor due to its rigid tetrahedral structure with no free electrons; graphite (Y) conducts electricity because of its layered structure with delocalised electrons.
Section B — Answers
2 marks each21.
Amphoteric nature of Al₂O₃: Al₂O₃ is amphoteric because it reacts with BOTH acids and bases to produce salt and water — behaving as a base towards acids and as an acid towards bases.
Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O
Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O
Marking: 1 mark for stating the amphoteric property correctly; 1 mark for a correct supporting equation (either one is sufficient).
22.
A balanced chemical equation has an equal number of atoms of each element on both the reactant and product sides. Equations must be balanced to satisfy the Law of Conservation of Mass — matter can neither be created nor destroyed in a chemical reaction.
Marking: 1 mark for definition; 1 mark for stating the law correctly.
23.
Any two of: (i) Painting the iron surface to keep out air and moisture. (ii) Oiling/greasing to form a protective barrier. (iii) Galvanisation — coating with zinc. (iv) Alloying — making stainless steel (Fe + Ni + Cr).
Marking: 1 mark for each correct method (any two), up to 2 marks.
24.
Roasting: Heating a sulphide ore strongly in excess air to convert it to an oxide. Example: 2ZnS + 3O₂ → 2ZnO + 2SO₂
Calcination: Heating a carbonate ore strongly in limited/absence of air to convert it to an oxide. Example: ZnCO₃ → ZnO + CO₂
Marking: 1 mark each for correct definition + example (roasting and calcination).
25.
Quick lime (CaO) absorbs moisture from air and reacts with it to form slaked lime — calcium hydroxide. This is a combination reaction.
CaO + H₂O → Ca(OH)₂
OR: Iron reacts with steam to form iron(III) oxide (magnetite, Fe₃O₄) and hydrogen gas. This is a combination/oxidation reaction.
3Fe + 4H₂O(g) → Fe₃O₄ + 4H₂
Marking: 1 mark for correct equation; 1 mark for correctly identifying the reaction type.
26.
In the reactivity series, zinc lies above hydrogen while copper lies below hydrogen. Only metals above hydrogen can displace it from dilute acids to liberate H₂ gas. Since copper is less reactive than hydrogen itself, it cannot displace H₂ from dilute HCl, whereas zinc — being more reactive — readily does so.
Marking: 1 mark for correctly relating to reactivity series position; 1 mark for clear explanation.
Section C — Answers
3 marks each27.
Corrosion is the gradual deterioration of a metal's surface due to chemical reaction with substances in its environment (air, moisture, acids).
Conditions for rusting: Rusting of iron requires BOTH moisture (water) AND oxygen (air) to be present together. This is demonstrated using three test tubes containing iron nails: Tube A (nail + ordinary water, exposed to air) shows rusting; Tube B (nail + boiled/oxygen-free water sealed with oil) shows no rusting; Tube C (nail + dry air, using anhydrous CaCl₂ to absorb moisture) shows no rusting. This proves that BOTH air and water together are essential for rust to form.
Marking: 1 mark for definition of corrosion; 2 marks for correctly describing the experimental conditions/conclusion.
28.
(a) A displacement reaction is one in which a more reactive element displaces a less reactive element from its compound/solution.
(b) Since iron is more reactive than copper (higher in the reactivity series), iron will displace copper from copper sulphate solution:
Fe + CuSO₄ → FeSO₄ + Cu
(c) This is a displacement reaction (specifically, a single displacement reaction).
Marking: 1 mark each for parts (a), (b) with correct equation, and (c).
29.
Sodium (electronic configuration 2,8,1) has one electron in its outermost shell. Chlorine (2,8,7) needs one more electron to complete its octet. When sodium and chlorine react, sodium transfers its outermost electron to chlorine.
Na (2,8,1) → Na⁺ (2,8) + e⁻
Cl (2,8,7) + e⁻ → Cl⁻ (2,8,8)
The resulting Na⁺ and Cl⁻ ions, being oppositely charged, are held together by strong electrostatic forces of attraction, forming the ionic compound sodium chloride (NaCl). (A labelled diagram should show the electron transfer arrow from Na to Cl, with dot-and-cross notation for the outer shells.)
Marking: 1 mark for correct electron configurations; 1 mark for correct electron transfer equations; 1 mark for diagram/explanation of electrostatic attraction.
30.
(a) An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal, prepared by melting the primary metal and dissolving other elements in it in definite proportions.
(b) Stainless steel = Iron + Nickel + Chromium. It is hard, strong, and does not rust — making it ideal for cutlery and surgical instruments.
(c) Alloying disrupts the regular arrangement of metal atoms in the lattice, which interferes with the free flow of delocalised electrons, thereby lowering electrical conductivity compared to the pure constituent metals.
Marking: 1 mark for each part (a), (b), (c).
31.
(a) 2Al + 3H₂O(g) → Al₂O₃ + 3H₂
(b) Ca + 2H₂O → Ca(OH)₂ + H₂
(c) ZnO + C → Zn + CO
Marking: 1 mark for each correctly balanced equation.
32.
Property 1 — Physical state: Metals are solids at room temperature (exception: mercury, which is liquid).
Property 2 — Lustre: Metals have a shiny/lustrous surface (exception: non-metal iodine also shows metallic lustre).
Property 3 — Conductivity: Metals conduct heat and electricity well (exception: graphite, a non-metal, also conducts electricity).
OR: The liquid used is likely a dilute acid (commonly nitric acid or aqua regia mixtures used by fraudsters), which dissolves some of the gold from the surface, removing the tarnished/dull outer layer and exposing a shinier layer beneath — but in the process, actual gold metal is dissolved away, causing a real reduction in weight. This is a classic case of an unscrupulous goldsmith using acid to "clean" jewellery while secretly stealing gold through dissolution.
Marking: 1 mark per correct property+exception pair (3 total), OR for the alternative: 1.5 marks for identifying the acid/liquid, 1.5 marks for the chemical explanation.
33.
(a) X has ionic (electrovalent) bonding.
(b) In the solid state, the ions of X are held rigidly in a fixed crystal lattice and cannot move, so no charge can be carried. When melted or dissolved in water, the lattice breaks down and the ions become free to move, allowing them to conduct electric current.
(c) A likely example is sodium chloride (NaCl) or any common ionic salt.
Marking: 1 mark each for (a), (b), and (c).
Section D — Answers
5 marks each34.
(a) Highly reactive metals (K, Na, Ca, Mg, Al) — extracted by electrolysis of their molten chlorides/oxides, since they have a greater affinity for oxygen than carbon and cannot be reduced by it. Example: Sodium, by electrolysis of molten NaCl.
Moderately reactive metals (Zn, Fe, Pb, Cu) — extracted by reduction of their oxides using carbon (after roasting/calcination converts sulphide/carbonate ores to oxides). Example: Zinc, via ZnO + C → Zn + CO.
Least reactive metals (Hg, Ag, Au, Cu in some cases) — often found in the free/native state, or extracted simply by heating their ores in air. Example: Mercury from cinnabar (HgS) by heating.
(b) Carbonate and sulphide ores must be converted to oxides because oxides are more easily reduced to the metal using carbon than carbonates or sulphides are; converting via roasting/calcination prepares the ore for efficient reduction.
OR:
(a) The activity/reactivity series is a list of metals arranged in order of decreasing reactivity. Decreasing order for the given metals: Sodium > Zinc > Iron > Copper > Gold.
(b) A more reactive metal can displace a less reactive metal from its salt solution because it has a greater tendency to lose electrons (form positive ions) than the less reactive metal. Example: Fe + CuSO₄ → FeSO₄ + Cu (iron displaces copper since it is more reactive).
(c) Copper and Gold do not react with dilute acids because both lie below hydrogen in the reactivity series — they lack sufficient reactivity to displace hydrogen from the acid.
Marking: 5 marks distributed across correct categorisation with examples (3 marks) and correct explanation of oxide conversion or displacement principle (2 marks).
35.
(a) Combination reaction: Two or more substances combine to form a single product. Example: 2Mg + O₂ → 2MgO
Decomposition reaction: A single compound breaks down into two or more simpler substances. Example: CaCO₃ → CaO + CO₂
Displacement reaction: A more reactive element displaces a less reactive one from its compound. Example: Zn + CuSO₄ → ZnSO₄ + Cu
(b) Balanced equations and reaction types:
(i) 3Fe + 4H₂O(g) → Fe₃O₄ + 4H₂ — Combination/oxidation reaction
(ii) CaCO₃ → CaO + CO₂ — Decomposition reaction
(iii) AgNO₃ + NaCl → AgCl + NaNO₃ — Double displacement (precipitation) reaction
Marking: 1 mark each for 3 definitions+examples (part a, max 3 marks shared); 2 marks for correctly balancing and identifying all three equations in part (b).
36.
(a) Ionic compounds are compounds formed by the transfer of electrons from a metal atom to a non-metal atom, resulting in oppositely charged ions held together by electrostatic forces. Example: formation of NaCl as described in Q29 — Na loses an electron to become Na⁺, Cl gains it to become Cl⁻.
(b) Four physical properties: (i) Hard and brittle solids. (ii) High melting and boiling points. (iii) Generally soluble in water, insoluble in kerosene/petrol. (iv) Conduct electricity only in molten or dissolved state, not as solids.
(c) Ionic compounds have high melting/boiling points because a considerable amount of energy is needed to overcome the strong electrostatic forces of attraction holding the oppositely charged ions together in the rigid crystal lattice.
OR:
(a) Anodising is an electrolytic process used to thicken the naturally occurring protective oxide layer on aluminium. It is carried out because it significantly improves aluminium's resistance to further corrosion, and the thicker layer can also be dyed for an attractive finish.
(b) Galvanisation is the process of coating iron/steel with a thin layer of zinc to prevent rusting. Even if the zinc coating is locally scratched, the article continues to resist rusting because zinc is more reactive than iron and corrodes preferentially, sacrificially protecting the exposed iron underneath (this is the principle of "sacrificial protection").
(c) Roasting converts a sulphide ore to an oxide by heating strongly in excess air (e.g. 2ZnS + 3O₂ → 2ZnO + 2SO₂). Calcination converts a carbonate ore to an oxide by heating strongly in limited/absence of air (e.g. ZnCO₃ → ZnO + CO₂).
Marking: 5 marks distributed across all three parts with roughly equal weighting; partial credit for correct definitions even without full explanation.
Section E — Answers (Case-Based)
4 marks each, 1 mark per sub-part37.
(a) Sodium is higher in the reactivity series than calcium, meaning it has a much greater tendency to lose its outermost electron and react. This makes its reaction with cold water far more vigorous and exothermic than calcium's.
(b) Calcium floats because the bubbles of hydrogen gas produced during the reaction stick to its surface, acting like tiny flotation aids that keep the metal piece afloat.
(c) Mg + 2H₂O(hot) → Mg(OH)₂ + H₂
(d) Decreasing order of reactivity: Sodium > Calcium > Magnesium > Copper
Marking: 1 mark for each correctly answered sub-part (a)–(d).
38.
(a) The gas produced is hydrogen (H₂).
(b) Zn + 2HCl → ZnCl₂ + H₂
(c) This is a displacement reaction (zinc displaces hydrogen from the acid).
(d) No — copper would NOT produce hydrogen gas with dilute HCl, because copper lies below hydrogen in the reactivity series and cannot displace it from the acid. No reaction would be observed.
Marking: 1 mark for each correctly answered sub-part (a)–(d).
39.
(a) The ions formed are the sodium cation (Na⁺) and the chloride anion (Cl⁻).
(b) In the solid state, Na⁺ and Cl⁻ ions are locked in a rigid crystal lattice and cannot move, so they cannot carry charge. When dissolved in water, the lattice breaks apart and the ions become free to move, allowing the solution to conduct electricity.
(c) Sodium chloride has a high melting point because a large amount of energy is required to overcome the strong electrostatic forces of attraction between the oppositely charged Na⁺ and Cl⁻ ions in the crystal lattice.
(d) Sodium chloride would NOT be soluble in kerosene. Ionic compounds are generally soluble only in polar solvents like water, and insoluble in non-polar solvents such as kerosene or petrol.
Marking: 1 mark for each correctly answered sub-part (a)–(d).
— End of Answer Key —
