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

Options

A. `K^(+) gt Na^(+) gt Rb^(+) gt Cs^(+)`
B. `Cs^(+) gt Rb^(+) gt K^(+) gt Na^(+)`
C. `Rb^(+) gt K^(+) gt Cs^(+) gt Na^(+)`
D. `Na^(+) gt K^(+) gt Rb^(+) gt Cs^(+)`

Answer

B

Explanation

The smaller the size of the ion, the greater is the degree of hydration, thus degree of hydration is highest of `Li^+` and lowest for `Cs^+`. Thus `Li^+` holds more water molecules in its hydration sphere and becomes largest in size among metals and `Cs^+` ion hold least number of water molecules .
Hence, ionic mobility is highest for `Cs^+` (due to its smallest size in aqueous solution ) and lowest for `Li^+`.Here the lowest is for `Na^+`. Thus, the order of ionic mobility in aqueous solution is
`Cs^(+) gt Rb^+ gt K^+ gt Na^+`