Which is the primary lymphoid organ?

The correct answer is Option (1) → Thymus

Option (1) Thymus — Correct. With the bone marrow, it is where immature lymphocytes become antigen-sensitive; T-lymphocytes mature here.

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

NCERT Extract:
Immune System in the Body – “… Lymphoid organs: These are the organs where origin and/or maturation and proliferation of lymphocytes occur. The primary lymphoid organs are bone marrow and thymus where immature lymphocytes differentiate into antigen-sensitive lymphocytes. After maturation the lymphocytes migrate to secondary lymphoid organs like spleen, lymph nodes, tonsils, Peyer’s patches of small intestine and appendix.”