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Identify the incorrect statement(s) among the following regarding alkali metals and their ions: (A) Among all alkali metal ions, Cs+ undergoes the greatest degree of hydration. (B) Among Li, Na, K, and Rb, lithium has the highest melting point. (C) The ionic mobility of Li+ is the greatest among all alkali metal cations. (D) The ionisation potential of lithium is lower than that of sodium.
- (A) Cs+ is more hydrated than the other alkali metal ions
- (B) Among the alkali metals Li, Na, K and Rb, lithium has the highest melting point
- (C) Ionic mobility of Li+ is maximum among alkali metal cations
- (D) Ionisation potential of Li is lower than that of Na
Correct answer: (A) Cs+ is more hydrated than the other alkali metal ions
Solution
Li+ has the smallest ionic radius and highest charge density, so it is the most hydrated alkali metal ion — not Cs+. Statement A is incorrect. Li does have the highest melting point among alkali metals (strong metallic bonding). Li+ has the lowest ionic mobility (large hydration shell). IP of Li > IP of Na (anomalous, due to small size and high nuclear attraction). So A, C, and D are incorrect; the question asks for incorrect ones.
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