41. Which of the following alkali metals has the lowest density?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) Cesium
Answer: (a) Lithium
Explanation: Lithium has the lowest density among alkali metals. The density increases as we move down the group, except for potassium, which is less dense than sodium due to its atomic structure.
42. Which of the following alkaline earth metals has the highest melting point?
- (a) Beryllium
- (b) Magnesium
- (c) Calcium
- (d) Strontium
Answer: (a) Beryllium
Explanation: Beryllium has the highest melting point among the alkaline earth metals due to its small size, strong metallic bonds, and high lattice energy.
43. Which of the following compounds is used as a drying agent in the laboratory?
- (a) Na₂CO₃
- (b) CaO
- (c) NaOH
- (d) MgSO₄
Answer: (b) CaO
Explanation: Calcium oxide (CaO), also known as quicklime, is a strong drying agent that readily absorbs moisture from the surroundings.
44. Which alkali metal reacts most vigorously with water?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) Cesium
Answer: (d) Cesium
Explanation: Cesium reacts explosively with water because it has a large atomic size and low ionization energy, which make it highly reactive. As we move down the group, the reactivity with water increases.
45. Which alkaline earth metal is commonly found in chlorophyll?
- (a) Magnesium
- (b) Calcium
- (c) Beryllium
- (d) Strontium
Answer: (a) Magnesium
Explanation: Magnesium is a central element in chlorophyll, the pigment that plants use for photosynthesis. It is coordinated with nitrogen atoms in the chlorophyll molecule.
46. Which of the following compounds is used as a desiccant in anhydrous form?
- (a) Na₂SO₄
- (b) CaSO₄
- (c) K₂SO₄
- (d) Li₂SO₄
Answer: (b) CaSO₄
Explanation: Anhydrous calcium sulfate (CaSO₄) is commonly used as a desiccant (drying agent) due to its ability to absorb water.
47. Which of the following elements forms an oxide used in the manufacture of Portland cement?
- (a) Barium
- (b) Calcium
- (c) Magnesium
- (d) Strontium
Answer: (b) Calcium
Explanation: Calcium oxide (CaO), derived from limestone, is a key ingredient in the manufacture of Portland cement. It reacts with other compounds to form clinker, which is then ground into cement.
48. Which of the following compounds does not undergo thermal decomposition easily?
- (a) Li₂CO₃
- (b) Na₂CO₃
- (c) K₂CO₃
- (d) Cs₂CO₃
Answer: (b) Na₂CO₃
Explanation: Sodium carbonate (Na₂CO₃) does not decompose easily upon heating. Lithium carbonate decomposes at a relatively lower temperature due to the smaller size of the lithium ion, which polarizes the carbonate ion.
49. Which of the following compounds is commonly known as washing soda?
- (a) Na₂CO₃
- (b) NaHCO₃
- (c) NaCl
- (d) NaOH
Answer: (a) Na₂CO₃
Explanation: Sodium carbonate (Na₂CO₃), commonly known as washing soda, is used in laundry detergents to soften water and enhance cleaning.
50. Which of the following alkaline earth metal chlorides is least soluble in water?
- (a) BeCl₂
- (b) MgCl₂
- (c) CaCl₂
- (d) BaCl₂
Answer: (a) BeCl₂
Explanation: Beryllium chloride (BeCl₂) has some covalent character due to the small size of the Be²⁺ ion, making it less soluble in water compared to the other chlorides, which are more ionic.
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