Some of the chapter which have a very high probability of coming in the JEE Main exam are as follows.

1. Semiconductors (Physics)

2. Work Power Energy (Physics)

3. Thermodynamics (Physics and Chemistry)

4. Electro-Chemistry

5. Solid State (Chemistry)

6. Conic Sections (Maths)

7. Environmental Chemistry

8. Biomolecules and Polymers (Chemistry)

So of the tough chapter that do not occur in the paper in large number of questions are:

1. Rotation

2. Center of Mass

3. Circular Motion

4. s-Block

5. Nitrogen derivatives

6. Salt analysis

7. Ionic equilibrium

8. Trigonometry

9. P&C

Hope I have answered your question. All the best!