CG Board Class 10 Science Chapter 9 Solutions: Metals and Metallurgy (धातु एवं धातुकर्म) (2026-27)

(i) Which among the following metals is most reactive:**

• (a) Mg
• (b) Al
• (c) Na
• (d) Zn

(c) Na

Explanation: Sodium (Na) lies near the top of the metal activity series, above Mg, Al, and Zn, making it the most reactive among the given choices.

Answer: (b) Al_2O₃ · 2H_2O

Explanation: Bauxite is the primary hydrated oxide ore of aluminium with formula Al_2O₃ · 2H_2O.

: (b) Al_2O₃ · 2H_2O

Answer: (c) Froth floatation

Explanation: Iron pyrite (FeS₂) is a sulfide ore, and sulfide ores are concentrated using the froth floatation process.

Answer: (c) Slag

Explanation: Calcium silicate (CaSiO₃) is formed when calcium oxide flux combines with silica impurity in the blast furnace, forming a molten fusible waste product called slag.

Answer: (b) Iron, chromium and nickel

Explanation: Stainless steel is an alloy composed mainly of iron (Fe), chromium (Cr ≈ 11.5\%), nickel (Ni ≈ 2\%), and traces of carbon.

(i) The process of removal of a less active metal from its salt solution by a more reactive metal is known as …………….. (displacement / precipitation) reaction.**

(ii) The primary iron ore found in Chhattisgarh is ……………….. (hematite / magnetite).

(iii) Alloys are a ……………………. (homogeneous / heterogeneous) mixture of two or more metal or metals and non-metals.

(iv) The process of heating an ore at a temperature a little below its melting point in the absence of oxygen is called …………………… (roasting / calcination).

• (i) displacement
• (ii) hematite
• (iii) homogeneous
• (iv) calcination

(i) Ore**

(ii) Mineral

(iii) Slag

(iv) Flux

(i) (Ore)

(iii) (Slag)

• (ii) Mineral: Inorganic chemical elements or compounds occurring naturally in the Earth’s crust with fixed chemical compositions and physical properties are called minerals.
• (iv) Flux: A chemical substance added to roasted ore during smelting to react with non-fusible gangue impurities and convert them into a fusible slag is called flux (e.g., Limestone CaCO₃ / CaO).
• (i) (Ore): ,
• (ii) (Mineral): , ,
• (iii) (Slag): ,
• (iv) (Flux):

(i) Reaction of aluminium metal with steam.**

(ii) Reaction of zinc oxide with sodium hydroxide.

(iii) Reaction when calcium carbonate is heated.

(iv) Reaction of oxygen with sodium.

(i)

(iii)

• (i) Aluminium with Steam:

2Al(s) + 3H_2O(g) → Al_2O₃(s) + 3H₂(g)↑

• (ii) Zinc Oxide with Sodium Hydroxide (Amphoteric nature):

ZnO(s) + 2NaOH(aq) → Na_2ZnO₂(aq) + H_2O(l)

(Product: Sodium Zincate)

• (iii) Thermal decomposition of Calcium Carbonate:

CaCO₃(s) → [Δ] CaO(s) + CO₂(g)↑

• (iv) Reaction of Sodium with Oxygen:

4Na(s) + O₂(g) → 2Na_2O(s)

• (i) :
• (ii) :
• (iii) :
• (iv) :

The process of obtaining free metal from its concentrated metal oxide is called reduction. The method chosen depends on the chemical reactivity of the metal

1. Carbon Reduction Method (Smelting):

• Medium reactive metals (like Fe, Zn, Pb, Sn) are reduced by heating their oxides with coke (carbon) or carbon monoxide at high temperatures (700°C-1800°C) in furnaces

ZnO + C → [Δ] Zn + CO↑

Fe_2O₃ + 3CO → [Δ] 2Fe + 3CO₂↑

1. Chemical Displacement Reduction:

• Metals can be reduced from their salt solutions or oxides using a more reactive metal (e.g., Al or Fe displacement)

CuSO₄ + Fe → FeSO₄ + Cu

1. Electrolytic Reduction:

• Highly reactive metals (Na, K, Ca, Al) cannot be reduced by carbon. Their molten salts are subjected to electrolysis, where pure metal ions reduce at the cathode

At Cathode: Mⁿ⁺ + ne^- → M(s)

Corrosion can be prevented by isolating the metal surface from moisture and oxygen

1. Barrier Protection:

• Applying a coat of paint, grease, oil, or varnish over the metal surface to block contact with air and moisture.

1. Galvanization (Sacrificial Protection):

• Coating iron objects with a thin layer of Zinc metal. Zinc reacts more readily with oxygen to form a protective layer of ZnO, protecting the underlying iron.

1. Electroplating:

• Depositing a layer of non-corrosive metal like chromium, nickel, or tin over iron using electric current.

1. Alloying:

• Mixing iron with chromium and nickel forms stainless steel, which does not rust.

1. Anti-rust Chemical Solutions:

• Applying basic phosphate or chromate solutions to form rust-resistant surface films.

For the electrolytic refining of a metal M

• Anode (Positive Electrode): A thick block/rod of the Impure metal M.
• Cathode (Negative Electrode): A thin sheet/rod of pure Metal M.
• Electrolyte: An aqueous solution of a soluble salt of the same Metal M (acidified if necessary).
• Example: Electrolytic Refining of Copper (Cu):
• Anode: Impure copper block.
• Cathode: Pure copper strip.
• Electrolyte: Acidified Copper Sulphate solution (CuSO₄ + dil. H_2SO₄).
• Reaction at Anode (Oxidation): Cu(s) → Cu²⁺(aq) + 2e^
• Reaction at Cathode (Reduction): Cu²⁺(aq) + 2e^- → Cu(s)
• Insoluble impurities settle below the anode as Anode Mud.

(i) Gravity separation method**

(ii) Froth flotation method

(iii) Magnetic separation method

(i)

(iii)

• (i) Gravity Separation Method:
• Principle: Based on the difference in specific gravities (densities) of ore and gangue particles.
• Process: Finely powdered ore is placed on an inclined vibrating table and washed with a strong stream of running water. Heavy ore particles settle in grooves, while lighter gangue particles get washed away (used for carbonate and oxide ores like Hematite Fe_2O₃).
• (ii) Froth Flotation Method:
• Principle: Based on preferential wetting characteristics (ore particles are wetted by oil, gangue by water).
• Process: Powdered sulphide ore is mixed with water and pine oil in a tank. Compressed air is blown to produce froth. Sulphide ore particles attach to air bubbles and float as froth to the top, while gangue settles (used for sulphide ores like ZnS, CuFeS₂).
• (iii) Magnetic Separation Method:
• Principle: Based on magnetic properties of either the ore or gangue impurities.
• Process: Powdered ore is passed over a conveyor belt running over magnetic rollers. Magnetic particles stick near the roller and drop into one bin, while non-magnetic particles fly off into a separate bin (used for separating magnetic impurities from Tin ore SnO₂).
• (i) :
• (ii) :
• (iii) :

(i) Concentration of ore**

(ii) Reduction of oxide to metal (along with chemical equation)

(iii) Diagram of blast furnace

(i)

(iii)

• (i) Concentration of Ore:
• Hematite (Fe_2O₃) is crushed and concentrated using the Gravity Separation Method to wash away lighter silica impurities.
• It is then roasted in air to remove volatile impurities like sulfur and arsenic as oxides (S + O₂ → SO₂↑, 4As + 3O₂ → 2As_2O₃↑).
• (ii) Reduction of Oxide to Metal (in Blast Furnace):
• Concentrated ore, limestone (CaCO₃), and coke (C) are fed from the top of the Blast Furnace while hot air is blown from the bottom.
• Reactions in different temperature zones:

1. Combustion Zone (400°C-900°C): C + O₂ → CO₂, CO₂ + C → 2CO
2. Reduction Zone (400°C-900°C): Fe_2O₃ + 3CO → 2Fe + 3CO₂↑
3. Slag Formation Zone (900°C-1200°C): CaCO₃ → CaO + CO₂↑, CaO + SiO₂ → CaSiO₃ (Slag)
4. Molten iron collects at the bottom as Pig iron.

• (iii) Blast Furnace Structure Scheme:
• Cylindrical steel tower lined with fireproof refractory bricks, featuring top cup-cone feeder, waste gas exit, hot air tuyeres, upper slag tap, and lower molten iron tap.
• (i) :
• (ii) :
• (iii) :

Rusting of iron is an electrochemical phenomenon. When iron is exposed to moist air containing O₂ and CO₂, tiny electrochemical cells form on its surface

1. Anode Region:

• Pure iron acts as the anode, losing electrons and oxidizing to Fe²⁺ ions

Anode: Fe(s) → Fe²⁺(aq) + 2e^

1. Cathode Region:

• Electrons travel through the metal to another region with higher oxygen concentration (cathode), where water and dissolved oxygen accept electrons

Cathode: 2H_2O(l) + O₂(g) + 4e^- → 4OH^-(aq)

1. Rust Formation:

• Fe²⁺ ions combine with OH^- ions to form ferrous hydroxide, which further oxidizes in atmospheric oxygen to form hydrated ferric oxide (Rust)

Fe²⁺ + 2OH^- → Fe(OH)₂(s)

2Fe(OH)₂(s) + 1/2O₂(g) + xH_2O(l) → Fe_2O₃ · xH_2O(s) (Rust)

(i) Gold, silver and platinum are used in making jewelry.**

(ii) Sodium, potassium and lithium metals are stored under kerosene.

(iii) Although aluminium is an active metal it is still used to prepare cooking utensils.

(iv) Carbonate and sulphide ores are converted into their oxides for extraction of metal.

(i) ,

(iii)

• (i) Gold, silver, and platinum possess brilliant luster, high malleability/ductility, and lie at the bottom of the activity series (unreactive), meaning they do not tarnish or corrode in air, water, or acids.
• (ii) Sodium, potassium, and lithium are highly reactive alkali metals. They react violently and exothermically with atmospheric oxygen and moisture at room temperature, catching fire. Storing them under non-reactive kerosene prevents air contact.
• (iii) Aluminium rapidly forms a tough, thin, protective transparent oxide layer (Al_2O₃) on its surface when exposed to air. This non-porous layer prevents further corrosion. Additionally, aluminium is lightweight, durable, and an excellent thermal conductor.
• (iv) It is chemically much easier to reduce a metal oxide to free metal using carbon or carbon monoxide than it is to reduce metal carbonates or sulphides directly.
• (i) , , ,
• (ii) ,
• (iii) (Al_2O₃) ,
• (iv)