81. Which of the following compounds is known as bleaching powder?
- (a) CaO
- (b) CaCO₃
- (c) Ca(OH)₂
- (d) Ca(OCl)₂
Answer: (d) Ca(OCl)₂
Explanation: Bleaching powder is calcium hypochlorite (Ca(OCl)2)(Ca(OCl)2), which is used as a disinfectant and bleaching agent.
82. Which alkali metal is the least reactive?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) Cesium
Answer: (a) Lithium
Explanation: Lithium is the least reactive alkali metal due to its small size and relatively high ionization energy, making it less reactive compared to the other alkali metals.
83. Which of the following alkaline earth metal salts is commonly used in fireworks?
- (a) Magnesium chloride
- (b) Calcium sulfate
- (c) Strontium nitrate
- (d) Barium sulfate
Answer: (c) Strontium nitrate
Explanation: Strontium salts, particularly strontium nitrate (Sr(NO3)2)(Sr(NO3)2), are used in fireworks to produce a bright red flame.
84. Which alkali metal is used as a coolant in nuclear reactors?
- (a) Sodium
- (b) Potassium
- (c) Lithium
- (d) Rubidium
Answer: (a) Sodium
Explanation: Liquid sodium is used as a coolant in nuclear reactors due to its excellent thermal conductivity and high heat capacity.
85. Which of the following alkaline earth metals is used in lightweight alloys?
- (a) Calcium
- (b) Beryllium
- (c) Strontium
- (d) Barium
Answer: (b) Beryllium
Explanation: Beryllium is used in lightweight alloys for aerospace applications because of its low density, high strength, and corrosion resistance.
86. Which alkali metal forms the most stable carbonate?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) Cesium
Answer: (b) Sodium
Explanation: Sodium carbonate (Na2CO3)(Na2CO3) is more stable than lithium carbonate, which decomposes upon heating, and potassium and cesium carbonates are highly soluble and reactive.
87. Which of the following alkaline earth metals forms an insoluble sulfate?
- (a) Beryllium
- (b) Magnesium
- (c) Calcium
- (d) Barium
Answer: (d) Barium
Explanation: Barium sulfate (BaSO₄) is insoluble in water and is used in medical imaging because of its low toxicity and opacity to X-rays.
88. Which of the following alkali metals has the highest melting point?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) Cesium
Answer: (a) Lithium
Explanation: Lithium has the highest melting point among the alkali metals due to its small atomic size and strong metallic bonds.
89. Which alkaline earth metal hydroxide is the least soluble in water?
- (a) Be(OH)₂
- (b) Mg(OH)₂
- (c) Ca(OH)₂
- (d) Ba(OH)₂
Answer: (a) Be(OH)₂
Explanation: Beryllium hydroxide (Be(OH)2)(Be(OH)2) is amphoteric and the least soluble in water compared to the other alkaline earth metal hydroxides.
90. Which of the following alkali metals does not form a superoxide?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) Cesium
Answer: (a) Lithium
Explanation: Lithium does not form a superoxide because its small size and high ionization energy favor the formation of simple oxides (Li2O)(Li2O).
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