Antibody is represented by:

The correct answer is Option (2) → H₂L₂

An antibody is a protein made by B-lymphocytes against a pathogen. Each antibody molecule has four peptide chains: two short light (L) chains and two long heavy (H) chains. So it is written as H₂L₂.

(1) H₁L₁ — Incorrect. This shows only two chains. An antibody has four.

(2) H₂L₂ — Correct. Two heavy chains and two light chains.

(3) H₁L₂ — Incorrect. An antibody has two heavy chains, not one.

(4) H₃L₁ — Incorrect. An antibody has two chains of each kind, not three heavy and one light.

Note: A similar question was also asked in CUET (UG) 2026 on 15-05-2026 (Slot 1), and in CUET (UG) 2025 on 26-05-2025 (Slot 2).

NCERT Extract:
Acquired Immunity – “… The B-lymphocytes produce an army of proteins in response to pathogens into our blood to fight with them. These proteins are called antibodies. The T-cells themselves do not secrete antibodies but help B cells to produce them. Each antibody molecule has four peptide chains, two small called light chains and two longer called heavy chains. Hence, an antibody is represented as H₂L₂.”

Figure 7.4 Structure of an antibody molecule