NCERT books play very important role in your JEE preparation. It is recommended book for your preparation.

Chemistry

NCERT textbooks are the most crucial material to refer for JEE Chemistry. Almost 60-75 % of the questions are directly taken from NCERT textbook for Chemistry. Inorganic Chemistry has most questions from NCERT.

Mathematics

Mathematics is regarded as the hardest section to crack in JEE Main and make it a point that you do ample practice to be able to answer as many questions as possible, asked in this section. This is one reason why NCERT Mathematics is the best for CBSE board exams, but not definitely not sufficient for JEE Mains.

Physics

For Physics you need a deep understanding of the subject. So, you should refer NCERT book.

You can easily qualify JEE Main if you read from NCERT books.

All the Best!!