Question

Abundance of element in human body in descending order are:
(A) O, C, H, N
(B) H, C, O, N
(C) C, O, H, N
(D) H, O, C, N

Answer 1

To answer this question, you must recall the substances that compose the human body. These substances are water and biomolecules namely, fats, proteins, carbohydrates and DNA. The major constituents of the biomolecules are carbon, oxygen, hydrogen and nitrogen.

Complete step by step solution
First we must discuss the major elements that constitute the human body. Almost 99% of the mass off the body is due to four major elements that are, carbon, hydrogen, nitrogen and oxygen. Let us discuss the amounts and presence of these elements.
Oxygen is the most essential atom that aids in supporting life. It is the main constituent of a water molecule which constitutes more than half of the human body. Owing to this, 65% of the body is made up of oxygen.
Carbon is the main component of the majority of organic compounds. It forms the backbone of all organic molecules namely, proteins, fats, carbohydrates, etc. Carbon content in the body is around 18%
Hydrogen is a chief constituent of water other than oxygen. It is also present in all organic molecules like proteins, carbohydrates, etc.
Nitrogen is found in the molecules of proteins, DNA and amino acids. Total nitrogen content in the body is 1%.
The order for abundance of elements in the human body in descending order is O, C, H, N.
The correct answer is A.

Note
Apart from these four major elements, the other main elements that constitute the human body are calcium and phosphorus. They compose the bones and skeletal system of the body. Other important elements present in the body are potassium, magnesium, sodium, magnesium and sulphur.