What is the main difference between an organic molecule and an inorganic molecule?

Answer 1

Organic molecules have carbon chains with oxygen, hydrogen, and nitrogen primarily.

Answer 2

The chain of an organic molecule is made of carbon only. The carbons may bond to many elements, but mostly S, O, H and N.

Inorganic molecules do NOT have a carbon chain/backbone. That's why we say humans are carbon based.

Carbon is a good backbone molecule because it can form four stable bonds. Silicon is generally thought to be another candidate molecule for such backbones, and scientists look for the presence of Si on other planets as possible evidence of life.