Which element is most abundant in living organisms?

• A. Nitrogen
• B. Hydrogen
• C. Oxygen
• D. Carbon

Answer: (D)

Carbon is the most abundant element in living organisms primarily due to its fundamental role as the backbone of biological molecules. It has the unique ability to form four covalent bonds with other atoms, allowing for a diverse range of complex structures. This tetravalency enables carbon to create large, stable molecules like proteins, nucleic acids, lipids, and carbohydrates, which are essential for life.

In addition to its bonding versatility, carbon's ability to form stable chains and rings contributes to the complexity and functionality of biomolecules. While hydrogen, nitrogen, and oxygen are also critical components of biological molecules, carbon's prevalence and versatility make it foundational to all known forms of life. This makes carbon the key element that underpins the chemistry of life, leading to its classification as the most abundant element in living organisms.