Boron always forms covalent compound.
The small size of `B^(3+)` favours formation of covalent compound.

Answer

A

Explanation

Boron always forms covalent bonds because boron required very high energy to form a tripositive ion. Due to its very small size, `B^(3+)` has high polarising power , so it forms covalent linkage according to Fajans' rule.