21. Which of the following alkali metal salts is used as a table salt?
- (a) KCl
- (b) NaCl
- (c) LiCl
- (d) CsCl
Answer: (b) NaCl
Explanation: Sodium chloride (NaCl), commonly known as table salt, is used in daily life for food seasoning and preservation. It is an essential part of the human diet.
22. Which of the following statements is incorrect regarding alkali metals?
- (a) Alkali metals are highly electropositive.
- (b) Alkali metals have low ionization energies.
- (c) Alkali metals form basic oxides.
- (d) Alkali metals readily form covalent compounds.
Answer: (d) Alkali metals readily form covalent compounds.
Explanation: Alkali metals form ionic compounds, not covalent compounds, due to their high electropositivity and tendency to lose an electron easily.
23. Which of the following alkaline earth metals does not form nitrates directly?
- (a) Magnesium
- (b) Calcium
- (c) Beryllium
- (d) Strontium
Answer: (c) Beryllium
Explanation: Beryllium, due to its small size and high charge density, forms compounds with covalent character and does not form nitrates directly like other alkaline earth metals. It usually reacts with nitrogen to form beryllium nitride (Be₃N₂).
24. Which alkali metal forms the least soluble carbonate?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) Cesium
Answer: (a) Lithium
Explanation: Lithium carbonate (Li₂CO₃) is the least soluble among alkali metal carbonates due to the small size of the lithium ion, which causes a high lattice energy.
25. Which of the following statements is true about magnesium and calcium?
- (a) Both form amphoteric oxides.
- (b) Both are used in fireworks.
- (c) Both react with water at room temperature.
- (d) Both are used in the manufacture of cement.
Answer: (b) Both are used in fireworks.
Explanation: Magnesium burns with a bright white flame and is used in fireworks, while calcium compounds impart an orange-red color to fireworks. Both are used for pyrotechnic purposes.
26. Which of the following statements is correct regarding the solubility of alkaline earth metal sulfates?
- (a) Solubility increases down the group.
- (b) Solubility decreases down the group.
- (c) Solubility remains constant down the group.
- (d) Solubility first increases and then decreases.
Answer: (b) Solubility decreases down the group.
Explanation: The solubility of alkaline earth metal sulfates (e.g., BeSO₄, MgSO₄, CaSO₄, etc.) decreases as we move down the group due to the decreasing hydration energy.
27. Which of the following compounds is used as a drying agent?
- (a) NaOH
- (b) CaCl₂
- (c) KOH
- (d) MgO
Answer: (b) CaCl₂
Explanation: Calcium chloride (CaCl₂) is hygroscopic and can absorb water vapor from the atmosphere, making it a good drying agent.
28. Which alkali metal hydroxide is used in the manufacture of soaps?
- (a) LiOH
- (b) NaOH
- (c) KOH
- (d) CsOH
Answer: (b) NaOH
Explanation: Sodium hydroxide (NaOH), also known as caustic soda, is used in the manufacture of soaps by saponifying fats and oils.
29. Which of the following elements forms an oxide that is used in the manufacture of refractory bricks?
- (a) Magnesium
- (b) Calcium
- (c) Sodium
- (d) Potassium
Answer: (a) Magnesium
Explanation: Magnesium oxide (MgO) has high thermal stability and is used in the manufacture of refractory bricks, which can withstand high temperatures.
30. 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 alkali metals due to its small atomic size, which results in stronger metallic bonds.
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