Hello,
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Not that you should focus on one subject. You should focus on all the 3 subjects which are very much important for passing out.
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Here are some of the best books for all the 3 subjects which you should prepare.
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For physics,

• Concepts of physics volume 1 and 2 by HC Verma
• Fundamentals of physics by halliday
• Understanding physics by DC Pandey
• Problems in physics by IE irodov

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For chemistry,

• NCERT books of 11 and 12
• Modern approach to chemical calculation by DC mukherjee
• Organic chemistry by OP Tandon
• Concepts of physical chemistry by p Bahadur

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Books for maths,

• Objective mathematics by RD Sharma
• Plane trigonomentry by loney
• The elements of coordinate geometry by Loney
• Algebra by Dr SK goyal  arihant
• Differential calculus and intergral calculus by Amit Agarwal

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Here are the books and there authors which are best for learning and completing your preparation.
So, once you are done with this, have completed your preparation.
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If want to know other important topics then refer the below provided link,
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https://engineering.careers360.com/articles/best-books-for-jee-main

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