Comment on each of the following:
(a) The mobilities of alkali metal ions in aqueous solution are:
${{Li}^{+}}$ < ${{Na}^{+}}$ < ${{K}^{+}}$ < ${{Rb}^{+}}$ < ${{Cs}^{+}}$
(b) Lithium is the only metal to form nitride directly.
© BaO is soluble but BaS${{O}_{4}}$ is insoluble in
water.
