Dear Ankit,

In JEE Exam, Physics questions are asked from both Intermediate first and Second year syllabus. There is no particular most important chapter But make sure to cover these chapters from first year.

• Laws of Motion
• Rotational Dynamics
• Gravitation
• Work power Energy.
• Simple harmonic motion
• Fluid dynamics
• Waves and Oscillations

Hello aspirant,

For MAINS almost every topic is importance because we often having at least one question from every topic across all sets of paper.

Some topics however form the babis of further learning and later become determental in your understanding of further topics. Let these be Category A.

Some other topics are simple and devoting a week can fetch you marks in MAINS but these topics are most of the time left put as theya re not main stream. Let these be category B.

Physics

A

• Laws of Motion
• Rotational Dynamics
• Gravitation ( same as electrostatics )

B

• Work, Power , Energy
• Circular Energy
• Simple Harmonic Motion ( guaranteed question )
• Fluid dynamics
• Oscillations and Waves ( study sincerely once, enjoy till JEE Adv )

All the Best!!!

Hey there

For selection every chapter is important but 

1. Newton's law of motion

2. Work power energy

3. Waves and oscillation.

4. Rotation.

5. Sound.

These are very important chapters from her mains point of view you should definitely have clear concepts of them. Though all chapters has to be done atleast an overview should be there.

Good luck