For getting selected in the prestigious IIT's, you require following qualifications

1. Among the top 20%ile in your respective X11th board.

2. Qualified JEE mains.

3. Qualified JEE advanced and should have a considerable rank within your category to expect a seat at IIT's

The extra subjects you'll study at IIT's entirely depends on what you branch you are studying.

But with every branch, you can expect studying about 28-35 subjects and each subject having aroung 6-7 chapters. These all subjects you'll cover in your entire 4 years curriculum.

I hope I've answered your request