The correct answer is option 4, Vitamin K. Vitamin K plays a crucial role in the clotting of blood. When bleeding occurs, vitamin K activates certain proteins in the blood that are responsible for the clotting process, ensuring that the bleeding stops. Without enough vitamin K, blood clotting may be impaired, leading to excessive bleeding.

Option 1, Vitamin A, does not directly contribute to blood clotting. Instead, it is vital for good vision, immune system health, and cell growth.

Option 2, Vitamin B, is a group of vitamins that have various functions in the body, but they do not specifically aid in blood clotting.

Option 3, Vitamin C, is necessary for the growth and repair of tissues, skin health, and boosts the immune system, but it does not have a direct role in blood clotting.

Therefore, the correct answer is option 4, Vitamin K.