Can you help me to decide wether to take admission in private college or drop a year for IIT .

If you really want any particular college then study for it and take a drop but if you think you cannot make it through studying then don't waste time, join a good college.

Frankly, I would request you not to drop a year for IIT. IIT is a wonderful institution, agreed. But be that as it may, dropping a year, under any circumstances, is not worth it. The JEE Advanced exam is not going to become any less competitive, and chances of getting in aren't going to be much bett