Comment on each of the following observations:
(a) The mobilities of the alkali metal ions in aqueous solution are `Li^(+)ltNa^(+) lt K^(+) lt Rb^(+) lt Cs^(+)`
(b) Lithium is the only alkali metal to form a nitride directly
(c) `E^(Theta)` for `M^(2+)` (aq) `+2e^(-)rarrM(s)` (where M=Ca, Sr or Ba) is nearly constant