Which vitamin is primarily involved in blood coagulation?

Vitamin K plays a crucial role in the process of blood coagulation, which is the body's mechanism for stopping bleeding. It is essential for the synthesis of certain proteins that are necessary for blood clotting, specifically prothrombin, which is a precursor to thrombin that is needed for the formation of blood clots. Without adequate vitamin K, the body cannot produce these clotting factors effectively, leading to an increased risk of excessive bleeding.

In contrast, vitamin A is primarily involved in vision, immune function, and skin health, while vitamin B12 is essential for red blood cell formation and neurological function. Vitamin C, known for its role in collagen synthesis and antioxidant properties, does not participate in the coagulation process. Thus, vitamin K is uniquely positioned as the vitamin directly associated with achieving proper blood clotting, making it the correct answer to the question.