Q.8 A protoxin is
(a) a primitive toxin                         

(b) a denatured toxin
(c) toxin produced by Protozoa     

(d) inactive toxin

(d) A protoxin is an inactive toxin. The word ‘pro’ in protoxin signifies ‘inactive form’ B.thuringiensis forms protein crystal is which contain a toxic insecticidal protein (Bt toxin).

Bt toxins are initially inactive protoxins but once ingested by insect, the inactive toxin, gets converted into an active form due to the alkaline pH of the gut which soiubilises the crystals.