The correct answer is option 1: Calcium. Calcium plays an important role in the coagulation of blood. Coagulation is the process by which blood forms clots to prevent excessive bleeding. When blood vessels are damaged, platelets in the blood aggregate at the site of injury and form a plug, which is then reinforced by a complex cascade of proteins called clotting factors. Calcium plays a crucial role in this cascade by activating several clotting factors, including Factor IV or ionized calcium.
Option 2: Iron is not involved in the coagulation process. Iron is important for the production of red blood cells and the transportation of oxygen in the blood.
Option 3: Potassium is not directly involved in the coagulation process. Potassium is an electrolyte that is important for nerve and muscle function, including maintaining a regular heart rhythm.
Option 4: Sodium is also not directly involved in the coagulation process. Sodium is an electrolyte that helps maintain fluid balance in the body and nerve and muscle function.
Therefore, the correct answer is option 1: Calcium, as it plays a crucial role in the coagulation of blood.