Question

The ionic mobility of alkali metal ions in an aqueous solution is maximum for:

• A. $N{a}^{+}$
• B. $K^{+}$
• C. $R{b}^{+}$
• D. $L{i}^{+}$

Answer 1

Answer: (C)

$R{b}^{+}$

We know that smaller the size of an ion, higher is its mobility.

$L{i}^{+}$ is the smallest in size and hence, its mobility is the highest. However, this is not true in aqueous solution. In aqueous solution, ions gets hydrated due to which their size increases.

Since $L{i}^{+}$ has the highest charge density, it is hydrated the most, while $R{b}^{+}$ is hydrated the least.

Hence, the effective hydrated size of $L{i}^{+}$ is more than that of $R{b}^{+}$ and so, the ionic mobility of $R{b}^{+}$ is more than $L{i}^{+}$.

Option C is correct.