Where do immature lymphocytes differentiate and mature?

The correct answer is Option (3) → Bone marrow and thymus

Lymphoid organs are of two kinds. In the primary lymphoid organs, lymphocytes are formed and mature. In the secondary lymphoid organs, the mature lymphocytes meet antigens and multiply into effector cells.

Option (1) Spleen and lymph nodes — Incorrect. The spleen and lymph nodes are secondary lymphoid organs. Lymphocytes come here only after they have matured.

Option (2) Liver and kidneys — Incorrect. The liver and kidneys are not lymphoid organs. The liver works in metabolism and the kidneys in excretion.

Option (3) Bone marrow and thymus — Correct. The bone marrow and the thymus are the primary lymphoid organs. The bone marrow produces all blood cells, including lymphocytes, and the thymus gives the setting in which T-lymphocytes develop and mature.

Option (4) Tonsils and appendix — Incorrect. The tonsils and the appendix are secondary lymphoid organs, like the spleen and lymph nodes.

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.”