61. Which of the following is the most basic oxide?
- (a) Li₂O
- (b) Na₂O
- (c) K₂O
- (d) Cs₂O
Answer: (d) Cs₂O
Explanation: As we move down the alkali metal group, the basicity of oxides increases. Cesium oxide (Cs₂O) is the most basic among alkali metal oxides due to the large size and lower electronegativity of the cesium ion.
62. Which of the following alkaline earth metals forms a water-insoluble hydroxide?
- (a) Beryllium
- (b) Magnesium
- (c) Calcium
- (d) Barium
Answer: (d) Barium
Explanation: Barium hydroxide (Ba(OH)2)(Ba(OH)2) is slightly soluble in water, but it is much less soluble than the hydroxides of calcium and magnesium. Solubility of hydroxides increases down the group, but barium hydroxide is sparingly soluble compared to the lighter alkaline earth hydroxides.
63. Which of the following metals forms a peroxide when heated in oxygen?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) Cesium
Answer: (b) Sodium
Explanation: Sodium forms sodium peroxide (Na₂O₂) when heated in excess oxygen, while other alkali metals like potassium and cesium form superoxides (MO2)(MO2) under similar conditions.
64. Which of the following alkaline earth metal sulfates is the most soluble in water?
- (a) BeSO₄
- (b) MgSO₄
- (c) CaSO₄
- (d) BaSO₄
Answer: (a) BeSO₄
Explanation: Beryllium sulfate (BeSO₄) is the most soluble in water among the alkaline earth metal sulfates. The solubility of sulfates decreases as we move down the group.
65. Which of the following alkali metals has the highest tendency to form a superoxide?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) Cesium
Answer: (d) Cesium
Explanation: Cesium, due to its large size and low ionization energy, has the highest tendency to form superoxides (CsO₂) compared to other alkali metals.
66. Which of the following elements forms an oxide that is used in the treatment of cancer?
- (a) Barium
- (b) Calcium
- (c) Magnesium
- (d) Radium
Answer: (d) Radium
Explanation: Radium, due to its radioactivity, is used in the treatment of certain types of cancer. Radium oxide is one of its compounds used for radiotherapy.
67. Which alkali metal ion is commonly used in salt substitutes for people on low-sodium diets?
- (a) Li⁺
- (b) Na⁺
- (c) K⁺
- (d) Cs⁺
Answer: (c) K⁺
Explanation: Potassium chloride (KCl) is commonly used as a salt substitute for individuals on low-sodium diets because potassium is essential for the body and does not raise blood pressure like sodium.
68. Which of the following alkaline earth metals is the least reactive towards water?
- (a) Beryllium
- (b) Magnesium
- (c) Calcium
- (d) Strontium
Answer: (a) Beryllium
Explanation: Beryllium does not react with water under normal conditions due to the formation of a passivating oxide layer, making it the least reactive alkaline earth metal towards water.
69. Which of the following alkali metal compounds is used as an antacid?
- (a) NaHCO₃
- (b) Na₂CO₃
- (c) K₂CO₃
- (d) Li₂CO₃
Answer: (a) NaHCO₃
Explanation: Sodium bicarbonate (NaHCO₃), commonly known as baking soda, is used as an antacid to neutralize stomach acid and relieve indigestion and heartburn.
70. Which alkaline earth metal forms a nitrate that decomposes to give nitrite and oxygen?
- (a) Calcium
- (b) Magnesium
- (c) Barium
- (d) Strontium
Answer: (c) Barium
Explanation: Barium nitrate (Ba(NO₃)₂) decomposes upon heating to form barium nitrite (Ba(NO₂)₂) and oxygen. This is a common decomposition pattern for nitrates of heavier alkaline earth metals.
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