Comment on each of the following observation:
a. The mobilities of the alkali metal ions in aqueous solution are `Li^(o+)ltNa^(o+)ltK^(o+)ltRb^(o+)ltCs^(o+)`.
b. Lithium is the only alkali metal to form a nitride directly.
c. `E^(ө)` for `M_(aq)^(2+)+2e^(-)to M_((s))` (where M=Ca,Sr or Ba) is nearly constant.