Which of the following element cannot exceeds the covalency more than four.

[Step 1]:Electronic configuration of carbon is (1S)2(2S)2(2P)2[Step 2]:Due to absence of d-orbitals, the orbitals available for carbon are only 2S, 2Px, 2Py and  2PZ for bonding.Therefore, the maximum covalency of carbon is four..[Step 3]:While Al, Si and P are belongs to third period for them d-orbitals are available for  bonding and they show covalency more than four.