NEET 2021 Chemistry Question 79 Solution

According to Fajan's rules, covalent character in an ionic compound increases with: 1. Small size of the cation 2. High positive charge on the cation 3. High charge-to-size ratio (polarizing power)

Beryllium ($Be^{2+}$) has an exceptionally small ionic radius (approximately $31\text{ pm}$), giving it an extraordinarily high polarizing power compared to $Mg^{2+}, Ca^{2+}, Sr^{2+},$ and $Ba^{2+}$. It strongly polarizes the electron clouds of adjacent chloride anions, pulling electron density into the internuclear region and imparting strong covalent character.

Because $BeCl_2$ is essentially covalent and non-ionic, it does not form an expansive ionic crystal lattice that requires polar water for hydration. Instead, following the "like dissolves like" principle, it dissolves readily in non-polar and moderately polar organic solvents such as ether, benzene, and alcohols, whereas chlorides of $Mg, Ca,$ and $Sr$ are ionic and insoluble in non-polar organic solvents.