Mark the pair of substances among the following which is essential for coagulation of blood.
(a) Heparin and calcium ions
(b) Calcium ions and platelet factors
(c) Oxalates and citrates
(d) Platelet factors and heparin
Calcium ions and platelets facilitate the conversion of fibrinogen into fibrin so that the blood can coagulate. The answer is the option (b) calcium ions and platelet factors.