(B) does not react with oxygen even at high temperatures

Gold is the least reactive metal. As stated in the textbook, "Silver and gold do not react with oxygen even at high temperatures," making gold chemically stable and ideal for jewellery.

Source: Chapter 3, Section 3.2.1

The key reason gold is used in jewellery is its chemical inertness — it does not tarnish or corrode. While gold is highly malleable and ductile, option (A) is factually incorrect (gold is the most ductile, but not the most malleable — gold and silver share top malleability). Silver and copper are better conductors than gold, ruling out (C). Option (D) is also false. Examiners expect you to recall the specific line about gold/silver not reacting with oxygen even at high temperatures.

(C) Hydrogen

When calcium reacts with cold water, hydrogen gas is evolved. The bubbles of H₂ stick to the metal's surface, making calcium float.

$$\text{Ca(s)} + 2\text{H}_2\text{O(l)} \rightarrow \text{Ca(OH)}_2\text{(aq)} + \text{H}_2\text{(g)}$$

Source: Chapter 3, Section 3.2.2

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The key fact is that all metals reacting with water produce hydrogen gas, not oxygen or CO₂. The floating is caused by H₂ bubbles clinging to the metal surface — a detail specifically mentioned for calcium in the textbook. Examiners may test whether students confuse the gas evolved (H₂) with the product in solution (Ca(OH)₂).

(B) Impure copper block

In electrolytic refining of copper, the impure copper block is used as the anode, pure copper strip as the cathode, and acidified copper sulphate solution as the electrolyte.

Source: Chapter 3, Section 3.4.6 (Refining of Metals)

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The textbook clearly states: "the impure metal is made the anode and a thin strip of pure metal is made the cathode." Examiners expect you to know all three components (anode, cathode, electrolyte) for this topic, even if the question asks only about one. Option (A) is the cathode, (C) is the electrolyte, and (D) is never used here.

(C) Bromine

Bromine is the only non-metal that exists as a liquid at room temperature. All other non-metals are either solids or gases.

The textbook (Section 3.1.2) explicitly states: "The non-metals are either solids or gases except bromine which is a liquid." Sulphur, iodine, and phosphorus are all solids at room temperature. This is a direct fact-based question — just recall the exception.

(B) 3:1 (HCl : HNO₃)

Aqua regia is a mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1 (HCl : HNO₃).

The term aqua regia (Latin for "royal water") is mentioned in NCERT as it can dissolve noble metals like gold. The ratio 3:1 (HCl : HNO₃) is a standard fact students must memorise — note that HCl is taken in greater proportion. This is a direct recall question; no derivation needed.

(C) Roasting

Roasting is the process of heating a sulphide ore strongly in excess air to convert it into its oxide.

Roasting specifically applies to sulphide ores heated in excess air. Calcination (option A) involves heating carbonate/hydroxide ores in limited air. Students often confuse these two — remember: Sulphide → Roasting; Carbonate → Calcination.

(C) Copper

Copper does not react with dilute hydrochloric acid because it lies below hydrogen in the reactivity series.

The reactivity series (Table 3.2, Chapter 3) places copper below hydrogen, meaning it cannot displace hydrogen from dilute acids. The textbook explicitly states: "In the case of copper, no bubbles were seen and the temperature also remained unchanged. This shows that copper does not react with dilute HCl." Zinc, iron, and magnesium all lie above hydrogen and do react with dilute HCl to produce hydrogen gas.

(C) Solder

An alloy of lead and tin used for welding electrical wires is called Solder.

Solder is a well-known alloy of lead and tin with a low melting point, making it ideal for joining electrical wires. Brass is copper + zinc; Bronze is copper + tin; Steel is iron + carbon. For MCQs, eliminate the wrong options by recalling alloy compositions.

(C) Presence of both air and water

Iron rusts only when exposed to both air (oxygen) and water simultaneously, as shown in Activity 3.14 — nails in dry air or boiled water (without air) did not rust.

Source: Chapter 3, Section 3.5 Corrosion

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The textbook Activity 3.14 clearly demonstrates that nails rust only in test tube A (air + water), not in B (water only, no air) or C (dry air, no water). Examiners expect you to select option C and may award a mark only for the correct option — no justification is needed in an MCQ, but knowing the reason helps if a follow-up short-answer appears.

(A) Na > Ca > Mg > Al > Zn

The reactivity series (Table 3.2, Chapter 3) lists metals in decreasing reactivity: K > Na > Ca > Mg > Al > Zn > Fe > … Option A is the only one that correctly follows this order. Memorise the reactivity series — it is frequently tested in MCQs and short-answer questions.

(B) Ions are mobile in the molten state but are rigidly held in solid state

In solid ionic compounds, ions are fixed in a rigid lattice and cannot move. On melting, electrostatic forces are overcome, ions move freely and conduct electricity.

Source: Chapter 3, Section 3.3.1 – Properties of Ionic Compounds

The textbook explicitly states: "Ionic compounds in the solid state do not conduct electricity because movement of ions in the solid is not possible due to their rigid structure. But ionic compounds conduct electricity in the molten state since the electrostatic forces of attraction between oppositely charged ions are overcome due to heat." Option B directly reflects this. Options A, C, and D are factually incorrect — solid ionic compounds do contain ions; melting neither generates new electrons nor creates covalent bonds.

(B) Copper is more reactive than silver.

Copper displaces silver from silver nitrate solution because it is more reactive, forming copper nitrate (solution turns blue) and silver deposits on the wire.

Source: Chapter 3, Section 3.2.4 & 3.2.5 (Reactivity Series)

In the reactivity series, copper is placed above silver, meaning copper is more reactive. A more reactive metal displaces a less reactive metal from its salt solution — this is a displacement reaction. The blue colour of the solution is due to Cu²⁺ ions (copper nitrate formed), and the shiny deposit is silver metal. Options A and C say the opposite and are wrong; D is incorrect as the metals clearly differ in reactivity.

(B) These metals have greater affinity for oxygen than carbon does

The textbook (Section 3.4.5) explicitly states: "carbon cannot reduce the oxides of sodium, magnesium, calcium, aluminium, etc., because these metals have more affinity for oxygen than carbon." This makes carbon ineffective as a reducing agent for these metals, so electrolysis is used instead. Option B is the reason, not just a consequence — examiners expect this conceptual distinction.

(A) Both A and R are true, and R is the correct explanation of A.

Aluminium is highly reactive but develops a thin, stable oxide (Al₂O₃) layer on exposure to air, which protects it from further corrosion, making it suitable for cooking utensils.

The textbook explicitly states that aluminium develops a thin oxide layer when exposed to air, making it resistant to further corrosion. This protective layer is the direct reason why a reactive metal like aluminium can still be used safely for everyday purposes like cooking utensils. Both the Assertion and Reason are factually correct, and the Reason directly explains the Assertion — so option (A) is correct. Examiners expect you to identify this cause-effect link clearly.

(A) Both A and R are true, and R is the correct explanation of A.

HNO₃ is a strong oxidising agent; it oxidises the H₂ produced to water, so hydrogen gas is not evolved when metals react with dilute nitric acid.

The examiner expects the student to know that nitric acid (dilute or concentrated) acts as an oxidising agent and oxidises nascent hydrogen to water, which is why H₂ gas is not liberated — unlike reactions with HCl or H₂SO₄. Both the assertion and the reason are factually correct, and the reason directly explains why hydrogen is not evolved, making option (A) the correct choice.

(A) Both A and R are true, and R is the correct explanation of A.

Ionic compounds have high melting and boiling points because a considerable amount of energy is required to break the strong electrostatic forces of attraction between oppositely charged ions.

Source: Chapter 3, Section 3.3.1 Properties of Ionic Compounds

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The textbook explicitly states: "Ionic compounds have high melting and boiling points. This is because a considerable amount of energy is required to break the strong inter-ionic attraction." Both the assertion and reason are factually correct, and the reason directly and correctly explains the assertion — so option (A) is the answer. Don't confuse this with covalent compounds, which have low melting/boiling points due to weak intermolecular forces.

(A) Both A and R are true, and R is the correct explanation of A.

Carbon cannot reduce Na₂O or Al₂O₃ because sodium and aluminium are more reactive than carbon and have greater affinity for oxygen, so carbon cannot displace them from their oxides.

The reactivity series places Na and Al above carbon. A more reactive metal has greater affinity for oxygen and cannot be displaced by a less reactive reducing agent like carbon. Thus R directly and correctly explains A — making option (A) the right choice. Remember: carbon can reduce oxides of metals below it in the reactivity series (e.g., ZnO, PbO), but not Na₂O or Al₂O₃.

With dilute HCl:
$$\text{ZnO} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2\text{O}$$

With sodium hydroxide:
$$\text{ZnO} + 2\text{NaOH} \rightarrow \text{Na}_2\text{ZnO}_2 + \text{H}_2\text{O}$$

Since zinc oxide reacts with both acids and bases, it is amphoteric in nature.

• The examiner expects both balanced equations (1 mark) and the term amphoteric with a one-line explanation (1 mark).
• "Amphoteric" is the key word — do not write just "neutral" or "dual nature" without naming it.
• The sodium zincate formula (Na₂ZnO₂) must be correct; some boards also accept ZnO + 2NaOH → Na₂[Zn(OH)₄] — either is acceptable as long as it is balanced.
• These reactions are a classic example from the Acids, Bases and Salts chapter (Class 10 Chemistry).

• With hot water: Magnesium reacts to form magnesium hydroxide and hydrogen gas.
• With steam: Magnesium reacts to form magnesium oxide and hydrogen gas.

Equation for reaction with steam:

$$\text{Mg(s)} + \text{H}_2\text{O(g)} \rightarrow \text{MgO(s)} + \text{H}_2\text{(g)}$$

Source: Chapter 3, Section 3.2.2

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• The key distinction: hot water → Mg(OH)₂ (hydroxide); steam → MgO (oxide). This difference is commonly tested.
• Examiners expect both products named for each case and the balanced chemical equation for steam specifically.
• Remember: Mg does not react with cold water at all — state this if asked.

Gangue: The earthly impurities such as soil and sand associated with an ore mined from the earth are called gangue.

Why it must be removed: If gangue is not removed before extraction, it will interfere with the extraction process, waste energy, and reduce the efficiency and purity of the metal obtained. Removal is done based on differences in physical or chemical properties between gangue and the ore.

Source: Metals and Non-metals, Section 3.4.2 Enrichment of Ores

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• The definition is directly from Section 3.4.2 — use the exact textbook phrasing for 1 mark.
• For the second part (1 mark), examiners expect you to state that impurities interfere with extraction and must be removed prior to it. Mentioning that separation uses differences in physical/chemical properties adds value.
• Do not over-explain; two crisp points are sufficient for 2 marks.

Galvanisation is a method of protecting iron and steel from rusting by coating them with a thin layer of zinc.

Even if the zinc coating is scratched, the iron beneath remains protected because zinc is more reactive than iron. Zinc corrodes preferentially (acts as a sacrificial metal), thereby preventing iron from rusting.

Source: Chapter 3, Section 3.5.1 – Prevention of Corrosion

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• Part 1 (definition) fetches 1 mark — state it concisely.
• Part 2 (reason) fetches the other 1 mark — the key idea is that zinc is more reactive than iron, so it oxidises first and protects iron even when the coating is broken. Examiners look for the phrase "more reactive" or "sacrificial protection." Don't just say "zinc forms a protective layer" — that only explains unscratched coating.

(i) Iodine is lustrous (shiny surface), whereas non-metals are generally non-lustrous.

(ii) Graphite conducts electricity, whereas non-metals are generally bad conductors of electricity.

Source: Metals and Non-metals, Section 3.1.2

The examiner expects one specific physical property for each exception — no elaboration needed. The key words are lustrous for iodine and conducts electricity for graphite. These are directly stated in the textbook as exceptions among non-metals. Avoid writing about chemical properties here; the question specifically asks for physical properties.

| | Roasting | Calcination |
|---|---|---|
| Definition | Heating sulphide or carbonate ores in excess of air below their melting point | Heating carbonate or hydroxide ores in limited/absence of air below their melting point |
| Product | Oxide of the metal + SO₂ gas | Oxide of the metal + CO₂ / water vapour |

Example of Roasting (sulphide ore of zinc):

$$2\text{ZnS} + 3\text{O}_2 \xrightarrow{\Delta} 2\text{ZnO} + 2\text{SO}_2$$

Example of Calcination (carbonate ore of zinc):

$$\text{ZnCO}_3 \xrightarrow{\Delta} \text{ZnO} + \text{CO}_2$$

Source: Metals and Non-metals, Extraction of Metals

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• Examiners expect one clear distinguishing point + one example each with a balanced equation — that earns all 3 marks.
• The key distinction is excess air (roasting) vs limited/no air (calcination), and sulphide ore vs carbonate/hydroxide ore.
• ZnS/ZnO and ZnCO₃/ZnO are the standard NCERT examples; you may also use Cu₂S or CaCO₃.
• Do not confuse calcination with decomposition in general — it is specifically applied to ores in metallurgy.

The thermit reaction is a displacement reaction between aluminium and iron(III) oxide:

$$\text{Fe}_2\text{O}_3 + 2\text{Al} \rightarrow \text{Al}_2\text{O}_3 + 2\text{Fe}$$

This reaction is highly exothermic — it releases a very large amount of heat (approximately 3000°C). The melting point of iron is about 1535°C, which is far lower than the heat produced. Therefore, the iron formed immediately melts and is obtained in the molten state, which flows into the gap between railway tracks and solidifies to join them firmly.

Source: Chapter 1 (Displacement Reactions); Chapter 3, Section 3.2.4

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• 1 mark: Correct balanced chemical equation.
• 1 mark: Stating the reaction is highly exothermic / releases enormous heat.
• 1 mark: Explaining that heat produced exceeds iron's melting point, so iron is obtained in molten form.

Examiners look for the equation written correctly (Fe₂O₃ + 2Al → Al₂O₃ + 2Fe) and a logical two-step explanation linking exothermic heat → temperature exceeds melting point of iron → molten iron. Don't just say "it's exothermic" — you must connect it to why iron melts.

Decreasing order of reactivity: P > S > Q > R

Identification of metals:

• P reacted vigorously with cold water, producing fire → Sodium (Na) (reaction is so violent and exothermic that hydrogen catches fire)
• Q reacted only with steam → Iron (Fe) or Aluminium (Al) (metals like aluminium and iron react only with steam, not cold or hot water)
• R did not react with water at all → Copper (Cu) (metals like copper, silver and gold do not react with water at all)

(S corresponds to Magnesium, which reacts with hot water but not violently.)

Source: Chapter 3, Section 3.2.2

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• The examiner expects the correct order first, then identification with brief justification for each.
• S (hot water only, not violently) = Magnesium — but the question only asks to identify P, Q, R, so mention S briefly or skip if marks are tight.
• For Q, either iron or aluminium is acceptable; iron is the most commonly cited textbook example.
• Always link each metal to its behaviour described in the question to earn full method marks.

Pure gold (24 carat) is too soft for jewellery, so it is alloyed with metals like copper or silver to make it harder and more durable.

22 carat gold means that out of 24 parts of the alloy, 22 parts are pure gold and 2 parts are other metals (such as copper or silver).

Effect of alloying on a pure metal:

• Electrical conductivity decreases — alloying reduces the conductivity of the pure metal.
• Melting point changes (generally decreases) compared to the pure metal.

• The question has three clear parts: (i) why gold is alloyed, (ii) meaning of 22 carat, and (iii) one general effect on conductivity AND melting point (the question says "one general effect" but lists two properties — address both briefly).
• Remember: an alloy is a homogeneous mixture, not a compound. Alloying improves hardness/strength but reduces electrical conductivity and often lowers melting point.
• 22 carat = 22/24 parts gold — state this as a fraction out of 24 to make it clear.

Copper reacts with moist carbon dioxide in the air, forming a green coating of basic copper carbonate on its surface. This is a corrosion reaction.

• The substance that tarnishes silver is silver sulphide — it is a sulphide (formed by reaction of silver with sulphur present in air). It is chemically a salt.
• The substance that tarnishes copper is basic copper carbonate — it is chemically a basic salt (or carbonate in nature).

Source: Chapter 3, Section 3.5 Corrosion

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• The question has two parts: (i) why copper develops a green coat (the reason/reaction), and (ii) the chemical nature of the tarnishing substances for both silver and copper. Address both clearly.
• Key fact: silver → silver sulphide (sulphide salt); copper → basic copper carbonate (basic salt/carbonate).
• Don't confuse: silver turns black (silver sulphide), copper turns green (basic copper carbonate). Examiners check whether you correctly name both compounds and their chemical nature.
• The word "basic copper carbonate" is expected verbatim from the textbook.

Three general physical properties of ionic compounds:

1. They have high melting and boiling points due to strong electrostatic forces between ions.
2. They conduct electricity in molten state or when dissolved in water (due to free ions).
3. They are generally hard and brittle solids at room temperature.

Why ionic compounds dissolve in water but not in non-polar solvents:
Water is a polar solvent. Its polar molecules interact with the positive and negative ions of ionic compounds, overcoming the ionic bonds and dissolving them. Non-polar solvents like petrol or kerosene cannot interact with ions in this way, so ionic compounds do not dissolve in them. The principle is "like dissolves like" — polar solvents dissolve ionic/polar compounds; non-polar solvents dissolve non-polar compounds.

Source: Chapter 3, Ionic Compounds; Chapter 4, Section 4.1

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• The textbook (Ch. 3 summary) directly states ionic compounds have high melting/boiling points and conduct electricity — use these confidently.
• The third property (hard and brittle) is standard CBSE content for ionic compounds from Ch. 3.
• For the dissolution part, the examiner expects the "like dissolves like" principle and the idea that polar water stabilises ions, while non-polar solvents cannot. This is a conceptual explanation, so 2–3 clear lines are enough — don't over-explain.
• Avoid copying carbon compound properties (low MP/BP, non-conductors) — those belong to covalent compounds.

(a) Reactivity Series and Grouping of Metals:
The reactivity series is a list of metals arranged in decreasing order of their reactivity (K, Na, Ca, Mg, Al, Zn, Fe, Pb, Cu, Hg, Ag, Au).

Based on this, metals are grouped into three categories for extraction:

• Low reactivity (Ag, Au, Hg) – found free in nature; extracted by heating alone.
• Medium reactivity (Zn, Fe, Pb, Cu) – extracted by reduction using carbon or displacement.
• High reactivity (K, Na, Ca, Mg, Al) – extracted by electrolytic reduction.

(b) Extraction of Medium Reactivity Metal from Sulphide Ore (e.g., Zinc from ZnS):

Step 1 – Roasting: Sulphide ore is heated strongly in excess air, converting it to the oxide:
$$2\text{ZnS(s)} + 3\text{O}_2\text{(g)} \xrightarrow{\text{Heat}} 2\text{ZnO(s)} + 2\text{SO}_2\text{(g)}$$

Step 2 – Reduction: The oxide is reduced with carbon (coke):
$$\text{ZnO(s)} + \text{C(s)} \rightarrow \text{Zn(s)} + \text{CO(g)}$$

(c) Carbon cannot reduce oxides of Na or Mg because these metals have a greater affinity for oxygen than carbon does, making carbon ineffective as a reducing agent here.

These metals are extracted by electrolytic reduction of their molten chlorides. For example, sodium is obtained by electrolysis of molten NaCl:

• At cathode: $\text{Na}^+ + e^- \rightarrow \text{Na}$
• At anode: $2\text{Cl}^- \rightarrow \text{Cl}_2 + 2e^-$

Source: Chapter 3, Sections 3.4.1, 3.4.4, 3.4.5

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• (a) Always define the reactivity series first, then list the three groups with examples — examiners look for both the definition and the classification.
• (b) The key steps are roasting (sulphide → oxide) then reduction with carbon. Write both equations; missing either loses marks.
• (c) The reason must be stated as "greater affinity for oxygen than carbon." Then name electrolytic reduction and give the electrode reactions — these are frequently asked and carry easy marks.

(a) Chemical Properties of Metals:

(i) Reaction with Oxygen:
Almost all metals react with oxygen to form metal oxides (basic in nature).
$$2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$$

(ii) Reaction with Water:
Metals react with water to form metal oxide/hydroxide and hydrogen gas. Reactivity varies — Na/K react with cold water, Mg with hot water, Al/Fe/Zn with steam; Cu does not react.
$$2\text{Na} + 2\text{H}_2\text{O} \rightarrow 2\text{NaOH} + \text{H}_2\uparrow$$

(iii) Reaction with Dilute Acids:
Metals above hydrogen in the activity series react with dilute acids to give salt and hydrogen gas.
$$\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2\uparrow$$

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(b) HNO₃ is a strong oxidising agent. It oxidises the H₂ produced to water and itself gets reduced to nitrogen oxides (NO, NO₂, N₂O). Therefore, hydrogen gas is not evolved when copper (or most metals) react with dilute HNO₃.

However, magnesium is highly reactive. When Mg reacts with very dilute HNO₃, the acid is too weak to oxidise all the H₂ produced, so hydrogen gas is evolved.

Source: Chapter 3, Section 3.2 (Chemical Properties of Metals)

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• Part (a) carries ~3 marks — one point + equation per reaction type. Keep equations balanced; examiners check this.
• Part (b) carries ~2 marks — the key phrase is "strong oxidising agent" for HNO₃, and "very dilute" for Mg's exception. Both must be stated.
• Common mistake: writing H₂ evolved for Cu + HNO₃ — it is NOT.
• The amphoteric oxide point (Al₂O₃, ZnO) is relevant for oxygen reactions but not required here unless asked specifically.

(a)

| Property | Metals | Non-metals |
|---|---|---|
| Physical state | Mostly solids at room temperature (except mercury, which is liquid) | Solids or gases (except bromine, which is liquid) |
| Malleability & Ductility | Malleable (beaten into sheets) and ductile (drawn into wires) | Neither malleable nor ductile; they are brittle |
| Electrical conductivity | Good conductors of electricity | Bad conductors (insulators) |

(b)
When magnesium burns, it forms magnesium oxide (MgO), a basic oxide — its solution turns red litmus blue. When sulphur burns, it forms sulphur dioxide (SO₂), an acidic oxide — its solution turns blue litmus red.

This indicates that metal oxides are basic in nature and non-metal oxides are acidic in nature.

Equations:
$$2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$$
$$\text{S} + \text{O}_2 \rightarrow \text{SO}_2$$

(c)

• Exception in metals (poor conductor): Mercury (or lead)
• Exception in non-metals (good conductor): Graphite (an allotrope of carbon)

Source: Chapter 3, Sections 3.1 and 3.2.1

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• For part (a), the table format earns full marks efficiently — state, malleability/ductility, and conductivity are the three specific heads asked.
• For part (b), examiners expect you to explicitly state the conclusion: metal oxides = basic; non-metal oxides = acidic. The two balanced equations are mandatory.
• For part (c), graphite (not just "carbon") is the expected answer for the non-metal exception, as stated in the textbook. Mercury is the most common metal exception for conductivity (though lead is also acceptable). The textbook specifically names graphite as the non-metal exception.

(i) Gold and silver are low in the reactivity series (least reactive), so they do not react with moisture or oxygen easily. Iron is higher in the reactivity series and thus more reactive, making it prone to rusting.

(ii) The green coating is basic copper carbonate, formed when copper reacts with moist CO₂ in air. It is a base, so it reacts with and dissolves in dilute acid (neutralisation reaction).

(iii) The mixture is called an alloy. Advantage: Pure gold (24 carat) is very soft; alloying with copper or silver makes it harder and more suitable for making jewellery.

(iv) The claim is incorrect. Iron requires both air (oxygen) and moisture to rust. In completely dry air, no moisture is present, so rusting will not occur (as shown by the iron nail in dry air remaining rust-free).

Source: Chapter 3, Section 3.5 Corrosion; Do You Know box (Alloys)

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• (i) Examiners expect mention of reactivity series positions — gold/silver are least reactive (bottom), iron is above them.
• (ii) The exact name "basic copper carbonate" is required; saying "it dissolves because it is basic/alkaline" earns the mark.
• (iii) "Alloy" is the keyword. The advantage must relate to hardness/durability, not just appearance.
• (iv) This is a direct application of Activity 3.14 — both air AND water are needed. Stating only one condition is insufficient.

(i) The process is called roasting. The sulphide ore is heated strongly in excess air to convert it into a metal oxide.

General equation: $2\text{MS} + 3\text{O}_2 \xrightarrow{\Delta} 2\text{MO} + 2\text{SO}_2$

(ii) It tells us that metal Y is low in the activity series (least reactive). Its oxide is unstable and is easily reduced by heat alone. Mercury (Hg) is one such metal.

(iii) Metal Z is deposited at the cathode (negatively charged electrode).

Half-reaction at cathode: $\text{Na}^+ + e^- \rightarrow \text{Na}$

(iv) The insoluble residue that settles at the bottom is called anode mud. It contains insoluble impurities from the impure metal, which may include precious metals like gold and silver.

Source: Chapter 3, Sections 3.4.3, 3.4.4, 3.4.5, 3.4.6

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• (i) Roasting = heating sulphide ore in excess air → metal oxide + SO₂. Don't confuse with calcination (carbonate ores, limited air).
• (ii) Key link: metals low in activity series → oxide easily decomposed by heat alone. Mercury is the textbook example (from cinnabar/HgS).
• (iii) Cathode is negative → attracts positive metal ions → metal deposited. The half-reaction given in the textbook uses Na⁺ (as metal Z is a very reactive metal extracted by electrolysis of molten chloride — fits Na/Mg/Ca).
• (iv) "Anode mud" is the exact CBSE term. Examiners expect both the name and that it contains insoluble/precious metal impurities.

(i) $\text{Fe}(s) + \text{CuSO}_4(aq) \rightarrow \text{FeSO}_4(aq) + \text{Cu}(s)$
This is a displacement reaction (iron displaces copper from copper sulphate solution).

(ii) Iron reacts with blue copper sulphate to form green iron sulphate (FeSO₄). As Cu²⁺ ions are replaced by Fe²⁺ ions, the blue colour fades and turns light green.

(iii) No reaction will occur. Copper is lower than iron in the activity series, so copper cannot displace iron from iron sulphate solution. No change will be observed in the solution or on the copper wire.

(iv) Yes, zinc can displace copper because zinc is more reactive than copper (higher in the activity series). The reaction is:
$$\text{Zn}(s) + \text{CuSO}_4(aq) \rightarrow \text{ZnSO}_4(aq) + \text{Cu}(s)$$

Source: Chapter 1, Section 1.2.3 Displacement Reaction

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• (i) The equation from the textbook (Eq. 1.24) is already balanced (1 Fe, 1 Cu, 1 S, 4 O on each side). Always name the reaction type.
• (ii) Focus on the ionic change: Cu²⁺ (blue) is replaced by Fe²⁺ (pale green). Examiners want both the chemical reason and the colour explanation.
• (iii) A common trap — students assume a reaction always occurs. The activity series rule works both ways: a less reactive metal cannot displace a more reactive one.
• (iv) Equation 1.25 from the textbook directly supports this. Zinc and lead are explicitly stated to be more reactive than copper.