Opsonization takes place through:

Ans. is 'b' i.e., C3b(Ref: Jawetz, 23rd/e, p. 121 - 123)* C3b and C4b are the major opsonins that coat the immune complexes and particulate Ags. Phagocytic cells have receptors for C3b, C4b and are able to bind to complement (C3b, C4b) coated Ags followed by phagocytosis.