Hello student!!

9 chapters have been rationalised from class 11 and 10 chapters from class 12.
Here are the topics which have been deleted.
Mathematics:
The principle of mathematical induction, binomial theorem, environmental chemistry, polymers, and chemistry in everyday life are chapters that have been completely deleted from the CBSE syllabus.
Physics
Physical world, Motion in a straight line, Laws of Motion, Gravitation, Mechanical Properties of Solids, Thermal properties matter, Thermodynamics, Waves and about 4 practicals have been deleted.

Chemistry:
Some topics from the States of Matter, Chemical Thermodynamics, equilibrium, S - Block Elements, Hydrocarbons, Solutions, Chemical Kinetics, Coordination Compounds, Amines, and Biomolecules have been deleted.
The topics deleted from the syllabus have significance in other chapters as well. The questions from this topic are usually asked in a mixed form using this concept from other chapters.

For more:
https://engineering.careers360.com/articles/how-deleted-cbse-syllabus-will-impact-jee-main-2021

Hello student ,

As the Deputy Chief Minister of Delhi mentioned that JEE Main 2021 will be based on the reduced syllabus of CBSE. Almost 30% of syllabus has been reduced for CBSE, and JEE Main 2021 aspirants can start preparing as per the revised syllabus. Further the official syllabus for JEE Main 2021 will be released soon. So i will suggest you to go through the official website of jee main to take update for the syllabus .

Hope it helps !