for chemistry nucleus chemistry is good.

Hi Kanti,

The best youtube channel for IIT-JEE prep is Khan Academy.

And the other preferred channels are Etoos Education, mlearning India, ExamFear education where you can find all the chapters completed with crystal clear explanation. They also provide sample examplar questions and answers. 

If you can efford, prefer BYJUS, they give wonderful explanations with many examples. You can view few samples video lectures even without paying for it.

Hope this helps.

All the best :)