Carbon compounds exist in large numbers due to the following reasons:

(a) Carbon exhibits catenation to a very large extent. Catenation is the ability of an atom to form chains or bonds with itself. It can form long chains, branched chains or ring structures.

(b) Carbon has a valency of 4. It is satisfied by forming single, double or triple bonds with carbon or other elements such as oxygen, hydrogen, nitrogen etc. The bonds formed are strong and hence the compounds formed are stable.