During the process of blood coagulation, vitamin K helps in the
A. Formation of thromboplastin
B. Formation of prothrombin
C. Conversion of prothrombin to thrombin
D. Conversion of fibrinogen to fibrin

Hint: Whenever we get injured and start bleeding after some time a clump of blood is observed in the wound and we stop bleeding this indicates the clotting of blood. The blood clotting takes place due to the blood coagulation process that involves many coagulation factors and proteins to carry out this process.

Complete Answer:
- The blood coagulation is the process in which blood is converted into insoluble gel when we get any wound or cut. The gel plugs leak the blood vessels that result in stopping the blood loss. This process requires phospholipids, calcium, and the coagulation factors.
- The coagulation factors are formed by the liver, the calcium is found in the blood and also through intracellular space, and the phospholipids are found in the platelet membrane. They give a surface for the reactions during the coagulation process.
- The coagulation process has two pathways; intrinsic pathway and extrinsic pathway. The intrinsic pathway starts inside the lumen of blood vessels, in this pathway, elements like calcium ions, clotting factors, and platelets that are found inside the vascular system and in extrinsic pathway, the tissue factor called thromboplastin is involves that releases when the wall of the vessels get ruptured.
- The initiation of intrinsic and extrinsic coagulation is different but once it gets completed they follow the common pathway. The common pathway comprises activation of factors like; factor X that is stuart power factor, factor V that is labile factor, factor II that is prothrombin, factor XIII that is fibrin stabilizing factor, and factor I that is fibrinogens involved. Both the pathways require to maintain hemostasis that results in providing positive feedback loops between both pathways.
- Now, vitamin K is a dietary vitamin that we get from food sources like animals and plants. This vitamin K is used by the liver in the production of factor II, factor VII, Factor IX, and factor X of coagulation process. The factor II is considered as a prothrombin that is made by the liver with the help of vitamin K.

Thus, the correct option is ‘B’. Formation of prothrombin.

Note: Any abnormality in the blood coagulation process may lead to many disorders. Like haemophilia, it is a rare genetic disorder that causes the lack of factor VIII that is antihemophilic factor. In this disorder the person does not undergo the clotting process and leads to bleeding for a long time if injured.