71. Which of the following alkali metals forms the least stable oxide?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) Cesium
Answer: (d) Cesium
Explanation: Cesium oxide (Cs₂O) is the least stable among alkali metal oxides due to the large size of the cesium ion and its relatively low lattice energy.
72. Which alkaline earth metal sulfate is used in medical imaging?
- (a) Beryllium sulfate
- (b) Magnesium sulfate
- (c) Calcium sulfate
- (d) Barium sulfate
Answer: (d) Barium sulfate
Explanation: Barium sulfate (BaSO₄) is insoluble and is used as a radiocontrast agent in X-ray imaging of the gastrointestinal tract because it absorbs X-rays well and is not absorbed by the body.
73. Which of the following alkali metals forms a highly soluble bicarbonate in water?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) Cesium
Answer: (b) Sodium
Explanation: Sodium bicarbonate (NaHCO₃) is highly soluble in water and is commonly used in baking, fire extinguishers, and as an antacid.
74. Which of the following alkaline earth metals forms a stable hydride?
- (a) Beryllium
- (b) Magnesium
- (c) Calcium
- (d) Barium
Answer: (b) Magnesium
Explanation: Magnesium hydride (MgH₂) is a stable compound used in hydrogen storage. It decomposes at high temperatures to release hydrogen gas.
75. Which of the following alkali metal halides is least soluble in water?
- (a) LiF
- (b) NaF
- (c) KF
- (d) CsF
Answer: (a) LiF
Explanation: Lithium fluoride (LiF) is the least soluble in water among the alkali metal halides due to the high lattice energy resulting from the small size of the lithium ion.
76. Which of the following alkaline earth metal oxides is amphoteric?
- (a) BeO
- (b) MgO
- (c) CaO
- (d) BaO
Answer: (a) BeO
Explanation: Beryllium oxide (BeO) is amphoteric, meaning it can react with both acids and bases. The other alkaline earth metal oxides are basic in nature.
77. Which of the following alkali metals is liquid at room temperature?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) None of these
Answer: (d) None of these
Explanation: None of the alkali metals are liquid at room temperature. All alkali metals are solid at room temperature, although they have relatively low melting points.
78. Which of the following compounds is used to de-ice roads in winter?
- (a) NaCl
- (b) KCl
- (c) CaCl₂
- (d) MgCl₂
Answer: (c) CaCl₂
Explanation: Calcium chloride (CaCl₂) is used to de-ice roads in winter because it lowers the freezing point of water and generates heat as it dissolves, making it effective in melting ice.
79. Which of the following elements forms the hardest oxide?
- (a) Lithium
- (b) Beryllium
- (c) Magnesium
- (d) Calcium
Answer: (b) Beryllium
Explanation: Beryllium oxide (BeO) is extremely hard and has a high melting point. It is used in specialized applications like ceramics and nuclear reactors due to its hardness and stability.
80. Which alkali metal hydroxide is the strongest base?
- (a) LiOH
- (b) NaOH
- (c) KOH
- (d) CsOH
Answer: (d) CsOH
Explanation: Cesium hydroxide (CsOH) is the strongest base among the alkali metal hydroxides due to the large size of the cesium ion, which makes it highly dissociable in water.
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