The alkali metals react with most non-metals to form hydrides, oxides, sulphides, carbides, phosphides and other compounds. The binary compounds of all alkali metals are ionic with `M^(+)` cations. The alkali metals easily ionize and readily reduce hydrogen ions. They react with ammonia to evolve hydrogen and form blue coloured solutions.
`2M(s) + 2H_2O (l) to 2MOH(aq) + H_2(g)`
`2M(s) + 2NH_3 (l) to 2MNH_2(am) + H_2(g)`
Arrange the following alkali metal ions in the decreasing order of their mobility in aqueous solutions:
`Li^(+), Na^(+),K^(+),Rb^(+)`

Explanation

`Rb^(+) gt K^(+) gt Na^(+) gt Li^(+)`