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Regarding Group 1 (alkali) metals, three statements are given below: (P) Among all alkali metal cations, Cs+ has the least degree of hydration. (Q) Among Li, Na, K and Rb, lithium has the highest melting point. (R) The ionic mobility of Li+ in aqueous solution is the lowest among all alkali metal cations because of its large hydrated radius arising from strong hydration. Which of the above statements are correct?

1. (P) and (Q) only
2. (Q) and (R) only
3. (P), (Q) and (R)
4. (P) only

Correct answer: (P), (Q) and (R)

Solution

Cs+ is the largest alkali cation, so it has the least charge density and smallest hydration shell — statement (P) is correct. Melting point of alkali metals decreases down the group, so Li has the highest — (Q) is correct. Li+ has the smallest bare radius but the largest hydrated radius due to strong hydration, giving it the lowest ionic mobility — (R) is correct.

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