- P. B cells are responsible for humoral immunity. They produce antibodies to neutralize pathogens. So, P matches with 1 (Humoral immunity).
- Q. Neutrophils are involved in phagocytosis. They are white blood cells that engulf pathogens and debris. So, Q matches with 4 (Phagocytosis).
- R. T cells are involved in cytotoxicity. They are responsible for killing infected or cancerous cells. So, R matches with 2 (Cytotoxicity).
- S. Mast cells are involved in histamine-associated allergy. They release histamines during allergic reactions. So, S matches with 3 (Histamine-associated allergy).
Step 1: Conclusion
The correct matching is (B) P-2, Q-4, R-1, S-3.