Which one of the following is the correct statement?

We examine every option one‐by‐one and keep only the correct statement.

Option A: Boric acid ($$H_3BO_3$$) behaves as a Lewis acid, not a proton-donating (Bronsted) acid. It accepts $$OH^-$$ from water to release $$H^+$$: $$H_3BO_3 + 2H_2O \rightarrow [B(OH)_4]^- + H_3O^+$$. Hence it is not a protonic acid. Option A is wrong.

Option B: Because of its very small ionic radius, $$Be^{2+}$$ generally attains tetrahedral coordination (CN = 4). Achieving a coordination number of 6 would require bond lengths that are too short to accommodate six ligands around the tiny $$Be^{2+}$$ centre. Therefore beryllium does not exhibit CN = 6. Option B is wrong.

Option C: In the solid state both $$BeCl_2$$ and $$AlCl_3$$ exist as polymeric species in which chloride ions bridge two metal centres. The typical fragments are $$\cdots\,Cl{-}Be{-}Cl{-}Be{-}Cl\,\cdots$$ and $$\cdots\,Cl{-}Al{-}Cl{-}Al{-}Cl\,\cdots$$ respectively. Thus they indeed possess bridged chloride structures. Option C is correct.

Option D: The compound nicknamed “inorganic benzene” is $$B_3N_3H_6$$ (borazine), not $$B_2H_6\cdot2NH_3$$. Option D is wrong.

Hence the only correct statement is:

Option C which is: Chlorides of both beryllium and aluminium have bridged chloride structures in solid phase