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

Carbon form large number of compounds due to the following properties: 

(a) Catenation → Carbon shows the property of catenation that is the ability to form bonds with other carbon atoms forming long chains both branched and unbranched chains, and even rings.

(b) Tetravalency → Carbon has valency 4, it is capable of bonding with 4 other carbon atoms or atoms of other non-covalent elements, giving rise to compounds with specific properties depending on the elements present in the compound. 

(c) Isomerism → Carbon compounds show the property of isomerism that is compounds having same molecular formula but different structural formula.