The most abundant element by number in the living system is :

Answer: Option B

In sequential order, Hydrogen, Oxygen, Carbon and Nitrogen are the most abundant elements by number in the living system. Hydrogen constitutes 49.8% of living systems, while Oxygen constitutes 24.9%; Carbon and Nitrogen account for 24.9% and 0.27% respectively. It is not surprising, therefore, that the living cell is between 60% and 90% water.