The valence shell electronic configuration of alkali metals is

Why are potassium and cesium,rather than lithium,used in photoelectric cells?

$A$ compound $(M_2O_2)$ of group $I$ element $(M)$ hydrolyses to form $M^{+}$,$OH^{-}$ and $X$. Another compound $(M'O_2)$ of group $I$ element $(M')$ hydrolyses to form $(M')^{+}$,$OH^{-}$,$X$ and $Y$. What are $X$ and $Y$ respectively?

Which of the following salts form hydrates? $CaCl_2$ $(I)$,$NaCl$ $(II)$,$LiCl$ $(III)$,$BaCl_2$ $(IV)$,$KCl$ $(V)$

In view of their low ionisation energies,the alkali metals are:

Which of the following is most soluble in water?