What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?

The 2 properties that makes carbon to form a very large number of compounds are:

1. Catenation: Catenation is the property of forming C-C chains to a large number of carbons. Besides Carbon, only Silicon has this property, but do not form such large compounds as that of carbon.
2. Tetravalency: Carbon has the Covalent nature with a valency of 4 which makes it to form numerous chain, ringed, Aromatic compounds by nature. Hence the number of carbon compounds exist in large numbers as compared to the compounds formed by all other elements.