Assertion : Fibrins are formed by the conversion of inactive fibrinogens on the plasma by the enzyme thrombin
Reason : Plasma without fibrinogen and blood corpuscles is called serum.

Answer: BSolution: A clot or coagulum is mainly formed of a network of threads called fibrins in which dead and damaged formed elements of blood are trapped. Fibrins are formed by the conversion of inactive fibrinogens in the plasma by the enzyme thrombin. Thrombins, in turn are formed from another inactive substance present in the plasma called prothromin, An enzyme complex, prothrombinasem is required for the above reaction.
The clot seals the wound and stops bleeding. After its formation, clot starts contracting and a pale yellow fluidm the serum, oozes out. This serum is blood plasma minus fibrinogen and blood corpuscles.