91. In the extraction of zinc from zinc blende, the ore is first concentrated by:
- A) Roasting
- B) Smelting
- C) Froth flotation
- D) Calcination
Answer: C) Froth flotation
Explanation: Zinc blende (ZnS) is concentrated using froth flotation before being roasted to convert it to zinc oxide for further processing.
92. The method used to refine metals like tin and lead is:
- A) Electrolysis
- B) Liquation
- C) Zone refining
- D) Froth flotation
Answer: B) Liquation
Explanation: Liquation is used to refine metals like tin and lead, which have low melting points, by melting and separating impurities.
93. The slag formed during the extraction of iron in the blast furnace is:
- A) SiO2
- B) FeSiO3
- C) CaSiO3
- D) Fe2O3
Answer: C) CaSiO3
Explanation: During the extraction of iron, calcium oxide reacts with silica to form calcium silicate (CaSiO3), which is removed as slag.
94. In the extraction of aluminium, the substance that lowers the melting point of alumina is:
- A) Sodium hydroxide
- B) Cryolite
- C) Calcium oxide
- D) Magnesium oxide
Answer: B) Cryolite
Explanation: Cryolite (Na3AlF6) is added to alumina to lower its melting point during the electrolytic extraction of aluminium.
95. The gas released during the roasting of zinc blende is:
- A) Carbon dioxide
- B) Sulphur dioxide
- C) Oxygen
- D) Nitrogen
Answer: B) Sulphur dioxide
Explanation: During roasting, zinc sulphide (ZnS) is heated in the presence of oxygen, releasing sulphur dioxide (SO2) gas.
96. Which of the following metals is obtained by the carbon reduction of its oxide?
- A) Aluminium
- B) Zinc
- C) Magnesium
- D) Copper
Answer: B) Zinc
Explanation: Zinc oxide is reduced by carbon in a furnace to obtain zinc metal in the extraction process.
97. In the Hall-Héroult process, the electrolyte used is:
- A) Sodium hydroxide
- B) Cryolite and alumina
- C) Zinc chloride
- D) Copper sulphate
Answer: B) Cryolite and alumina
Explanation: In the Hall-Héroult process, alumina (Al2O3) is dissolved in molten cryolite (Na3AlF6) to act as the electrolyte for the extraction of aluminium.
98. In the extraction of iron, carbon monoxide is produced by:
- A) The combustion of carbon
- B) The reaction of carbon with oxygen
- C) The reduction of carbon dioxide by carbon
- D) The reaction of carbon monoxide with iron ore
Answer: C) The reduction of carbon dioxide by carbon
Explanation: Carbon dioxide is reduced to carbon monoxide by reacting with coke (carbon) in the blast furnace.
99. The flux used in the smelting of copper to remove iron impurities is:
- A) Lime
- B) Silica
- C) Carbon
- D) Sodium carbonate
Answer: B) Silica
Explanation: Silica (SiO2) is used as a flux during the smelting of copper to remove iron as iron silicate slag.
100. The final product obtained after the electrorefining of copper is:
- A) Blister copper
- B) Matte
- C) Pure copper
- D) Copper oxide
Answer: C) Pure copper
Explanation: Electrorefining of copper results in the deposition of pure copper at the cathode, while impurities remain in the electrolyte or form anode sludge.
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