Biology · Biomolecules · NEET
Oxygen is the most abundant element by weight, about 65% of body mass. This is because our body is mostly water (H2O), and oxygen is a heavy atom compared to hydrogen. So even though water has 2 hydrogen atoms and only 1 oxygen atom, the oxygen weighs much more.
Oxygen > Carbon > Hydrogen > Nitrogen. In numbers: Oxygen ~65%, Carbon ~18%, Hydrogen ~10%, Nitrogen ~3%. This is the exact order the 2026 NEET paper asked. Learn it as O > C > H > N.
Life is 'carbon-based' because carbon forms the backbone of all organic molecules, not because carbon is the heaviest fraction. By weight, water pushes oxygen to the top. So carbon is second (~18%), important but not number one by mass.
Yes. By number of atoms, hydrogen is the most abundant because water and organic molecules have many light hydrogen atoms. But NEET usually asks 'by weight' or 'by mass', and then oxygen wins. Always read whether the question says weight or number.
All elements in living tissue are also in Earth's crust, but the relative amounts differ. In living tissue, carbon and hydrogen are much more abundant compared to other elements than they are in the crust. This higher relative abundance of C and H is a key NCERT point.
Arrange the following elements in descending order of their contribution to the percentage weight of the human body: (a) Oxygen, (b) Carbon, (c) Hydrogen, (d) Nitrogen.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Oxygen, Carbon, Hydrogen, and Nitrogen. Together they make up over 96% of body weight. The order by weight is O > C > H > N.
About 65% of the body's weight is oxygen, mostly held inside water molecules. This makes oxygen the single most abundant element by mass.
The body is roughly 70% water. Water is H2O, and oxygen atoms are heavy, so water pushes oxygen to the top of the weight list and also adds a lot of hydrogen.
Yes. NEET 2026 asked to arrange O, C, H, N in descending order of weight. The answer was Oxygen > Carbon > Hydrogen > Nitrogen, so this simple order is worth memorising.
