Best place or application to sell/donate JEE study material?

Hello

You can sell it at a fair price to shops that buys second hand books. Or you can sell them to someone who is not going to a tuition but wants the material. Or you can try selling it online on ShopClues, quickr, olx or fb.There are many study groups  on fb where you can post and sell books.Also there are few pages on fb which provides a selling platform.

But I would make a personal suggestion that don't sell it , give it to someone of class 11th/12th who is not wealthy enough to purchase books. That would help him in near future.

Regards
Careers 360