Hello student Generally students start preparing for Neet entrance examination in the beginning of class 11 but there's no definite time when you'll prepare enough for neet entrance examination it depends on your calibarity and vary from student to student. The syllabus of Neet entrance examination is the syllabus of class 11and 12 of Physics Chemistry and Biology so it'll be better if you start preparing for neet in class 11.

Prefer NCERT to build your basic concept and make sure you do each and every example and exercise questions of Ncert before jumping to a reference book, after completing ncert thoroughly refer to your coaching material or any reference book.

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Feel free to comment if you have any doubt

Good luck