How many of the following orders are correct? (i) Magnitude of hydration enthalpy: L i + N a + K + . (ii) Ionic mobility in water: L i + N a + K + . (iii) Reducing character in aqueous solutio

Question

How many of the following orders are correct?

(i) Magnitude of hydration enthalpy: $L i^{+} > N a^{+} > K^{+}$ .

(ii) Ionic mobility in water: $L i^{+} > N a^{+} > K^{+}$ .

(iii) Reducing character in aqueous solution: $Li < Na < K$ .

(iv) Thermal stability of carbonates: $L i_{2} C O_{3} < N a_{2} C O_{3} < K_{2} C O_{3}$ .

TestHub · Accepted Answer

(i) Correct: the smallest cation is hydrated most strongly, so the magnitude decreases down the group.

(ii) Incorrect: the strongly hydrated lithium ion is slowest.

The correct order is $L i^{+} < N a^{+} < K^{+}$ .

(iii) Incorrect: in water, lithium is the strongest and sodium the weakest of these reducing agents.

The correct order is $Li > K > Na$ , as shown by their standard reduction potentials.

(iv) Correct: thermal stability increases as cation size increases.

Only i and iv are correct, so the answer is 2.

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