The important element present in the living organism is carbon, hydrogen, nitrogen and oxygen. These elements are important for the formation of biomolecules of the living organism.
Barium is rarely found in organic molecules as barium is the alkaline earth metal. The barium is generally found in plants and rarely present in the living organism. Barium does not play such an important role as played by the other organic molecule. Hence, barium is rarely found in the living organism.
‘Noble gases’ are least reactive as their outer shells are fully filled with electrons. These do need to share their electrons from outer shells with other elements .