Due to the small size of ${\mathrm{Li}}^{+}$ ion and ${\mathrm{F}}^{-}$ions, the lattice energy of $\mathrm{LiF}$ is very high. $\mathrm{LiF}$ is covalent in nature. Therefore, $\mathrm{LiF}$ is insoluble in water.

${\mathrm{KO}}_2$  has $1$ unpaired electron in ${\mathrm{\pi }}^{\star }2\mathrm{p} \mathrm{Molecular} \mathrm{orbital}$ of ${\mathrm{O}}_2^{-}$ . Therefore, it is Paramagnetic.

 Lithium has lesser atomic weight than sodium. So, lithium has lesser density than sodium. But in the case of '$\mathrm{K}$' and '$\mathrm{Na}$', $\mathrm{d}$-orbitals present in Potassium, which increases the volume of '$\mathrm{K}$'.

Solution of sodium in liquid ammonia is conducting in nature, due to presence of free electron.