Question

Ionic mobility of which of the following alkali metal ions is the lowest when aqueous solution of their salts are put under an electric field?

• A. $Li$
• B. $Na$
• C. $K$
• D. $Rb$

Answer 1

The correct option is A $Li$

All the alkali metal ion exists as hydrated ions $M^{+}(H_{2}O{)}_n$ in it's an aqueous solution.

The degree of hydration decreases as the ionic size increases when we go down the group. Since the mobility of ions is inversely proportional to the size of their hydrated ions, the increasing order of ionic mobility is

$L{i}^{+}<N{a}^{+}<K^{+}<R{b}^{+}$