Question

Assertion :Among alkali metal cations, $L{i}^{+}(aq.)$ has highest electrical conductance. Reason: $L{i}^{+}(aq.)$ is largest alkali metal cation because of greater degree of hydration.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
• C. Assertion is correct but Reason is incorrect.
• D. Assertion is incorrect but Reason is correct.

Answer 1

The correct option is D Assertion is incorrect but Reason is correct.

It's the anomalous behaviour of Lithium because of its small size and high nuclear charge. Lithium exerts the greatest polarizing effect out of all the alkali metals on negative ion. It is the dissoloution of the substance in water by absorbing water molecule by weak valency forces. Smaller the cation, greater is the degree of hydration. Alkali metals easily lose 1 electron therefore have high values of "oxidising potential" which means high tendency to get oxidised. Hence, powerful reducing nature in aqueous medium. It is a fact that $L{i}^{+}$ has greatest reducing nature in aqueous medium due to maximum hydration energy for $L{i}^{+}$ ion.

Greater the degree of hydration, the mobility of ions is less, hence, it will have less electrical conductance. So, $L{i}^{+}$ has lowest electrical conductance.

Hence, option $D$ is correct.