Question

Ionic mobility of $L{i}^{+}$ is less than that of $N{a}^{+}$ and $K^{+}$ ions both, because:

• A. ionisation potential of Li is small
• B. charge density of $L{i}^{+}$ ion is high
• C. hydration tendency of $L{i}^{+}$ ion is high
• D. $L{i}^{+}$ has two electron

Answer 1

The correct option is C hydration tendency of $L{i}^{+}$ ion is high

The alkali metal ion exist as hydrated ions $M+(H_{2}O{)}_n$ in the aqueous solution. The degree of hydration, decreases with ionic size as we go down the group. Hence $L{i}^{+}$ ion is mostly hydrated e.g. $\left[Li\right(H_{2}O{)}_6{]}^{+}$. Since the mobility of ions is inversely proportional to the size of the their hydrated ions, hence the increasing order of ionic mobility is $L{i}^{+}$.