Prothrombin (Factor II) is one of the blood clotting factors . It is the precursor of the enzyme thrombin, which catalyses the formation of the fibrin matrix of the blood clot. Prothrombin synthesis occurs in the liver and is dependent on adequate supplies of vitamin K (fat soluble vitamin).The most common sources of vitamin K in diet are spinach ,broccoli ,iceberg, lettuce ,fats and oils, particularly soybean and canola oil
So the correct option is ‘Formation of prothrombin’.