What does CHNOPS stand for?
The acronym CHNOPS is often used to remember the 6 most common elements in living things: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. The first four of those (C, H, N, and O) are more common than the last two (P and S), so that's the simple answer to your question.
Since all life (or almost all life) is organically based, carbon is incredibly abundant in living things. Its flexible bonding allows it to make many types of molecules, including macromolecules like carbohydrates, proteins, lipids, and nucleic acids. Nitrogen is present in proteins, which make up a large percentage of the solid material of organisms' bodies. Hydrogen and oxygen are present in many macromolecules as well as being the constituents of water.