Which of the following orders is correct with respect to the magnitude of enthalpies of formation for alkali metal halides?

Which pair of metals dissolves in $NaOH$ solution?

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.
$(c)$ $E^{\circ}$ for $M^{2+}_{(aq)} + 2e^{-} \longrightarrow M_{(s)}$ (where $M = Ca, Sr$ or $Ba$) is nearly constant.

Why are lithium salts commonly hydrated and those of the other alkali metal ions usually anhydrous?

Which of the following oxides is not expected to react with sodium hydroxide?

Which of the following compounds has a negative enthalpy of solution?