1. Which of the following alkali metals forms the most stable peroxide?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) Rubidium
Answer: (c) Potassium
Explanation: Among alkali metals, potassium readily forms a stable peroxide. The stability of peroxides increases as we move down the group because the larger size of the cation stabilizes the large peroxide anion (O22−)(O22−). Potassium is larger than sodium and lithium, and hence forms a more stable peroxide.
2. Which of the following alkali metal ions is the smallest in size?
- (a) Li⁺
- (b) Na⁺
- (c) K⁺
- (d) Cs⁺
Answer: (a) Li⁺
Explanation: As we move down Group 1 (alkali metals), the size of the ions increases due to the addition of electron shells. Hence, the size order is Li⁺ < Na⁺ < K⁺ < Cs⁺. Lithium ion (Li⁺) is the smallest.
3. Which of the following alkaline earth metal carbonates is least soluble in water?
- (a) BeCO₃
- (b) MgCO₃
- (c) CaCO₃
- (d) BaCO₃
Answer: (d) BaCO₃
Explanation: The solubility of alkaline earth metal carbonates decreases as we move down the group. This is because the lattice energy decreases more slowly than the hydration energy. Therefore, BaCO₃ is the least soluble.
4. Which of the following compounds is used in the preparation of plaster of Paris?
- (a) MgSO₄
- (b) CaSO₄·2H₂O
- (c) BaSO₄
- (d) Na₂SO₄
Answer: (b) CaSO₄·2H₂O
Explanation: Plaster of Paris is chemically calcium sulfate hemihydrate (CaSO₄·½H₂O), which is prepared by heating gypsum, CaSO₄·2H₂O, to about 373 K. When water is removed partially from gypsum, it forms Plaster of Paris.
5. Which of the following is the correct order of ionization enthalpy for alkali metals?
- (a) Li > Na > K > Rb
- (b) Na > Li > K > Rb
- (c) K > Na > Li > Rb
- (d) Rb > K > Na > Li
Answer: (a) Li > Na > K > Rb
Explanation: As we move down the group in alkali metals, the ionization enthalpy decreases due to the increasing atomic size and the screening effect, which reduces the effective nuclear charge felt by the outermost electron. Hence, the correct order is Li > Na > K > Rb.
6. Which of the following alkaline earth metals does not impart color to the flame?
- (a) Beryllium
- (b) Magnesium
- (c) Calcium
- (d) Strontium
Answer: (a) Beryllium
Explanation: Beryllium and magnesium do not impart any color to the flame because their electrons are too tightly bound to be excited by the flame’s heat. Calcium, strontium, and other heavier alkaline earth metals do impart characteristic colors.
7. Which alkali metal is stored under kerosene oil?
- (a) Sodium
- (b) Magnesium
- (c) Calcium
- (d) Beryllium
Answer: (a) Sodium
Explanation: Sodium is highly reactive and readily reacts with moisture and oxygen in the air, so it is stored under kerosene oil to prevent it from reacting with air and water.
8. Which of the following oxides is amphoteric?
- (a) Na₂O
- (b) K₂O
- (c) BeO
- (d) MgO
Answer: (c) BeO
Explanation: Beryllium oxide (BeO) is amphoteric, meaning it can react with both acids and bases. Other oxides in the group, such as Na₂O and K₂O, are basic, while MgO is weakly basic.
9. Which of the following elements forms the most soluble hydroxide?
- (a) Lithium
- (b) Sodium
- (c) Potassium
- (d) Cesium
Answer: (d) Cesium
Explanation: The solubility of alkali metal hydroxides increases as we move down the group due to the decreasing lattice energy. Thus, cesium hydroxide (CsOH) is the most soluble.
10. Which of the following is a diagonal relationship observed in the periodic table?
- (a) Li and Be
- (b) Li and Mg
- (c) Na and Be
- (d) K and Ca
Answer: (b) Li and Mg
Explanation: The diagonal relationship refers to the similarity in properties between elements in different groups that are positioned diagonally to each other in the periodic table. Lithium (Group 1) shows similarities with magnesium (Group 2) due to comparable ionic radii and polarizing power.
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