The correct order of mobility of alkali metal ions in aqueous solution is

Options

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

Answer

C

Explanation

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