Question

Two carbon atoms cannot be linked to each other by more three covalent
bonds. Why?

Answer 1

The orbitals geometry around carbons cannot allow them to overlap in such a way to form fourbonds between them. 2px, 2py and 2pz orbitals are perpendicular to each other, this makes difficult for theorbitals two overlap with same atom

Answer 2

it is a special type of covalent bond between two atoms by which the atom which is more electronegative attracts more electrons from the bonded pair than the other atom.