When sodium is dissolved in liquid ammonia,a deep blue coloured solution is obtained. This colour of the solution is due to:

When $NaOH$ crystals are left in open air,they acquire a fluid layer around each crystal because:

The solubility of alkali metal fluorides increases down the group. Select the correct explanation for the given statement.

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.

Hydroxide of which alkali metal is used in the manufacture of soft soap?

Which among the following elements is used in devising photoelectric cells?