Chemistry - s Block Elements Question with Solution | TestHub

Mobility of alkali ions in aqueous solution $\propto \frac{1}{\text{ size of hydrated ion }}$

The mobility of alkali ions is inversely proportional to the size of ion in hydrated state, because bigger ion can't move faster. Also, small ion get hydrolysed to large exent due to which its size get increased. In other words, smaller ion will form hydrated ion of larger size.

Hence, correct order of mobility is

${\mathrm{Rb}}^{+}>{\mathrm{K}}^{+}>{\mathrm{Na}}^{+}>{\mathrm{Li}}^{+}$