Liquid sodium finds use in nuclear reactors. Its function is

$Na$ and $Li$ are placed in dry air. We get

Comment on each of the following observations:
$(a)$ The mobilities of the alkali metal ions in aqueous solution are $Li^{+} < Na^{+} < K^{+} < Rb^{+} < Cs^{+}$
$(b)$ Lithium is the only alkali metal to form a nitride directly.
$(c)$ The standard electrode potential $E^{\circ}$ for the reaction $M^{2+}_{(aq)} + 2e^{-} \to M_{(s)}$ (where $M = Ca, Sr$ or $Ba$) is nearly constant.

Write the decreasing order of hydration enthalpy of alkali metal ions.

Fill in the blanks:
$(1)$ $Li-Mg$ alloy is used to prepare ......
$(2)$ Colors of superoxides of alkali metals are ...... or ......
$(3)$ On combustion of lithium in the presence of air,it produces ...... and ......
$(4)$ On heating,lithium nitrate converts into ......

Discuss the diagonal relationship of lithium with magnesium.