The mobility of metal ions in aqueous medium (`Li^(o+), Na^(o+), K^(o+), Rb^(o+)`) in the electric field, follows the order.

Options

A. `Li^(oplus) gt Na^(oplus) gt K^(oplus) gt Rb^(oplus)`
B. `Rb^(oplus) gt Na^(oplus) -= K^(oplus) gt Li^(oplus)`
C. `Li^(oplus) lt Na^(oplus) lt K^(oplus) lt Rb^(oplus)`
D. `Na^(oplus) -= K^(oplus) gt Rb^(oplus) gt Li^(oplus)`

Answer

C

Explanation

Down the group with decrease in positive charge density of `M^(oplus)` on, tendency to get hydrated decreases and hence the size of hydrated ion decreases. Thus mobility increases. `Li_(aq) lt Na_((aq))^(oplus)lt K_((aq))^(oplus)lt Rb_((aq))^(oplus)`