Hi Kushagra,

I personally recommend these books for the preparation of  CUSAT 2020:-

@Physics

• Concepts of Physics Vol I &  II - H.C. Verma
• Understanding Physics - D.C Pandey

@Chemistry

• Concepts of Organic Chemistry For JEE - O.P Tandon
• A Textbook of Inorganic Chemistry For Competitions - O.P Tandon
• A Textbook of Organic Chemistry for JEE Mains and Advanced - Arihant Publications

@Mathematics

• Mathematics Volume I & II (Class XII) - R.D. Sharma

You may refer to this article for more information about CUSAT 2020.

I hope this information helps you.

Good Luck!