Explain why?

${\mathrm{BeCl}}_2$ shows a high degree of covalence in its reactions, whereas ${\mathrm{BaCl}}_2$ is predominantly ionic.

Explain why?

Carbon-Oxygen bond lengths in formic acid are $1.23 \mathrm{A}°$ and $1.36 \mathrm{A}°$ and both oxygen bonds in sodium formate have the same value, i.e. $1.27 \mathrm{A}°$.

In each of the following pairs, select the species having the greater stabilization:

${\mathrm{HNO}}_3$ and ${\mathrm{NO}}_3^{-}$.

In each of the following pairs, select the species having the greater stabilization:

 ${\mathrm{H}}_2\mathrm{C}=\mathrm{O}$ and ${\mathrm{H}}_2\stackrel{\left(+\right)}{\mathrm{C}}-\stackrel{\left(-\right)}{\mathrm{O}}$

Select the correct statement(s).

($\mathrm{I}$) Polarizability of ${\mathrm{S}}^{2-}$ is lower than ${\mathrm{Se}}^{2-}$
($\mathrm{II}$) Polarizability of ${\mathrm{S}}^{2-}$ is higher than ${\mathrm{Cl}}^{-}$
($\mathrm{III}$) Polarizability of ${\mathrm{S}}^{2-}$ is lower than ${\mathrm{P}}^{3-}$
($\mathrm{IV}$) Polarizability of ${\mathrm{O}}^{2-}$ is higher than ${\mathrm{S}}^{2-}$