Which of the following is/are the main factor(s) that enables carbon to form a large number of compounds?

Catenation and tetravalency are the main factors that enable carbon to form a large number of compounds.
The tendency of carbon to form chains of identical atoms is known as catenation. Carbon forms a long chain by combining with other atoms through covalent bonds. And in tetravalency, it has four valence electrons; It can form four covalent bonds with four different atoms, two double bonds, or a single and triple bond with other atoms.