Rahul gets a cut around his wrist such taht blood starts flowing out. rahul has a disorder due to which number of platelets in blood is low?

Hemophilia!

Hemophilia is a disease that prevents blood from clotting properly, so a person
who has it bleeds more than someone without hemophilia does.

For more info:
When most people get a cut, the body naturally protects itself. Sticky cells in the blood called platelets go to where the bleeding is and plug up the hole. This is the first step in the clotting process. When the platelets plug the hole, they release chemicals that attract more sticky platelets and also activate various proteins in the blood known as clotting factors. These proteins mix with the platelets to form fibres and these fibers make the clot stronger and stop the bleeding. Our bodies have 13 clotting factors that work together in this process (numbered using Roman numerals from I through XIII). Having too little of factors VIII (8) or IX (9) is what causes hemophilia. A person with hemophilia will only lack one factor, either factor VIII or factor IX, but not both.

Hope this helps!

It is used to during sexual reproduction between humans