51. Which alkali metal carbonate is used to remove permanent hardness of water?
- (a) Na₂CO₃
- (b) Li₂CO₃
- (c) K₂CO₃
- (d) Cs₂CO₃
Answer: (a) Na₂CO₃
Explanation: Sodium carbonate (Na₂CO₃), also known as washing soda, is used to remove permanent hardness of water by precipitating calcium and magnesium ions as their carbonates.
52. Which alkaline earth metal sulfate is least soluble in water?
- (a) BeSO₄
- (b) MgSO₄
- (c) CaSO₄
- (d) BaSO₄
Answer: (d) BaSO₄
Explanation: Barium sulfate (BaSO₄) is insoluble in water and is often used as a radiocontrast agent in medical imaging.
53. Which of the following compounds is used in the preparation of lime water?
- (a) CaCO₃
- (b) CaO
- (c) Ca(OH)₂
- (d) CaCl₂
Answer: (c) Ca(OH)₂
Explanation: Lime water is a dilute solution of calcium hydroxide (Ca(OH)₂) in water. It is used to test for carbon dioxide, as it turns milky when CO₂ is passed through it due to the formation of calcium carbonate.
54. Which of the following alkali metal ions has the highest hydration energy?
- (a) Li⁺
- (b) Na⁺
- (c) K⁺
- (d) Cs⁺
Answer: (a) Li⁺
Explanation: Lithium ion (Li⁺) has the highest hydration energy among alkali metals due to its small size and high charge density, making it strongly attracted to water molecules.
55. Which of the following elements is used in thermonuclear reactions?
- (a) Lithium
- (b) Sodium
- (c) Calcium
- (d) Magnesium
Answer: (a) Lithium
Explanation: Lithium is used in thermonuclear reactions as a source of tritium and as a material for fusion reactions.
56. Which of the following is a characteristic property of alkali metals?
- (a) They form acidic oxides.
- (b) They are good conductors of electricity.
- (c) They have high ionization energies.
- (d) They do not react with water.
Answer: (b) They are good conductors of electricity.
Explanation: Alkali metals are excellent conductors of electricity due to the presence of a single valence electron, which is easily delocalized.
57. Which alkaline earth metal carbonate decomposes on heating to give lime and carbon dioxide?
- (a) MgCO₃
- (b) CaCO₃
- (c) BaCO₃
- (d) SrCO₃
Answer: (b) CaCO₃
Explanation: Calcium carbonate (CaCO₃) decomposes on heating to form calcium oxide (lime, CaO) and carbon dioxide (CO2)(CO2).
58. Which of the following elements forms an oxide that is amphoteric?
- (a) Na
- (b) K
- (c) Be
- (d) Mg
Answer: (c) Be
Explanation: Beryllium oxide (BeO) is amphoteric, meaning it can react with both acids and bases, unlike other alkaline earth metal oxides, which are basic.
59. Which of the following compounds is commonly known as slaked lime?
- (a) CaO
- (b) Ca(OH)₂
- (c) CaCO₃
- (d) CaSO₄
Answer: (b) Ca(OH)₂
Explanation: Slaked lime is the common name for calcium hydroxide (Ca(OH)2)(Ca(OH)2), which is used in the preparation of lime water and in neutralizing acidic soils.
60. Which of the following elements has the smallest ionic radius in its group?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) Cesium
Answer: (a) Lithium
Explanation: Lithium has the smallest ionic radius among the alkali metals due to its small atomic size and fewer electron shells.
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