What common chemical features does all life have?

Answer 1

The four CHON elements are the primary components of life on Earth; Carbon, Hydrogen, Oxygen and Nitrogen. Chemistry involving these elements is called "organic chemistry", because so much of it is related to life-associated molecules.

It's possible (but unlikely!) that something like life may be based on a different chemistry; the most popular candidate would be silicon. Both carbon and silicon can form four molecular bonds to other atoms. But I feel that this would be unlikely, because the molecular bonds in carbon are much stronger than the molecular bonds in a silicon molecule.