The major function of platelets is option 1: clotting of blood. Platelets, also known as thrombocytes, play a crucial role in the process of hemostasis, which is the body`s mechanism to stop bleeding. When a blood vessel is damaged, platelets gather at the site and form a plug to prevent further blood loss. This process is known as primary hemostasis.

Platelets release various substances, such as thromboxane A2, serotonin, and ADP, which cause vasoconstriction and further recruitment of platelets. This creates a positive feedback loop, making the plug more stable and preventing bleeding.

Additionally, platelets also contribute to secondary hemostasis by releasing clotting factors and assisting in the formation of fibrin, a protein that strengthens the platelet plug and forms a clot. The formation of a clot helps to seal the damaged blood vessel and initiate the process of tissue repair.

Therefore, option 1 - clotting of blood - is the correct answer as it describes the primary and essential function of platelets in the body.