21. The Hall-Heroult process is used for the extraction of:
- A) Copper
- B) Zinc
- C) Aluminium
- D) Iron
Answer: C) Aluminium
Explanation: The Hall-Héroult process is the electrolytic method used for extracting aluminium from alumina. In this process, molten alumina is dissolved in molten cryolite and electrolyzed to obtain pure aluminium.
22. Which of the following reactions occurs in the blast furnace during the extraction of iron?
- A) C+O2→CO2
- B) CO2+C→2CO
- C) Fe2O3+3CO→2Fe+3CO2
- D) All of the above
Answer: D) All of the above
Explanation: All of these reactions occur in the blast furnace. Coke burns in oxygen to form carbon dioxide, which then reacts with more coke to form carbon monoxide, which finally reduces iron ore to iron.
23. Which of the following metals is extracted from its ore by the froth flotation method?
- A) Iron
- B) Aluminium
- C) Copper
- D) Zinc
Answer: C) Copper
Explanation: Froth flotation is used for the concentration of copper sulphide ores. The ore is crushed, mixed with water, and then treated with reagents to make the copper sulphide particles hydrophobic, so they attach to air bubbles and float.
24. The removal of sulphur from the molten metal in the extraction of copper is done by:
- A) Oxidation
- B) Reduction
- C) Leaching
- D) Electrolysis
Answer: A) Oxidation
Explanation: Sulphur is removed during the extraction of copper by oxidation. Sulphur combines with oxygen to form sulphur dioxide gas, which escapes.
25. Which of the following metals is not extracted using carbon as a reducing agent?
- A) Iron
- B) Copper
- C) Aluminium
- D) Zinc
Answer: C) Aluminium
Explanation: Aluminium is a highly electropositive metal, so it is extracted by electrolysis, not by reduction with carbon. Carbon is not a strong enough reducing agent to reduce aluminium oxide to aluminium.
26. In the blast furnace, the reducing agent responsible for converting iron oxide to iron is:
- A) Carbon
- B) Carbon monoxide
- C) Hydrogen
- D) Sodium
Answer: B) Carbon monoxide
Explanation: Carbon monoxide is the primary reducing agent in the blast furnace that reduces iron oxide to iron: Fe2O3+3CO→2Fe+3CO2
27. In the metallurgy of copper, the compound formed when copper pyrite (CuFeS2) is heated in the absence of air is:
- A) Copper sulphate
- B) Copper oxide
- C) Matte (Cu_2S and FeS)
- D) Copper metal
Answer: C) Matte (Cu_2S and FeS)
Explanation: When copper pyrite is heated in the absence of air, it forms matte, which is a mixture of copper(I) sulphide (Cu2S) and iron sulphide (FeS).
28. Which of the following processes is employed in the extraction of iron from iron ore?
- A) Smelting
- B) Electrolysis
- C) Froth flotation
- D) Leaching
Answer: A) Smelting
Explanation: Smelting is the process used to extract iron from its ore in a blast furnace. In this process, iron ore is heated with a reducing agent like carbon to obtain the metal.
29. In the extraction of iron, slag is formed by the reaction of:
- A) Iron oxide and silica
- B) Silica and calcium oxide
- C) Hematite and carbon monoxide
- D) Coke and iron oxide
Answer: B) Silica and calcium oxide
Explanation: Slag is formed by the reaction of silica (an impurity in the ore) with calcium oxide (obtained from limestone) to form calcium silicate: CaO+SiO2→CaSiO3CaO+SiO2→CaSiO3
30. Which of the following ores is concentrated by froth flotation?
- A) Bauxite
- B) Hematite
- C) Chalcopyrite
- D) Magnetite
Answer: C) Chalcopyrite
Explanation: Chalcopyrite (CuFeS2) is a sulphide ore of copper and is concentrated by froth flotation, a method specifically used for sulphide ores.
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