JEE Main

A. You should have grip at basics of all the chapters, because there are so many shifts so you can expect question from any chapter in any shift, at least you should know the formulas and the idea of how to apply them. B. Go through the NCRET book
Most important chapters for JEE Mains physics:
1. Semiconductor
2. Communication systems
3. Em waves
4. Thermodynamics
5. SHM
6. String and sound waves
7. Errors and measurement
8. Unit and dimensions
9. Kinematics
10. Modern and nuclear physics
11. Diffraction
12. Optical instruments
13. Elasticity and viscosity
14. Surface tension
15. AC current
16. Calorimetry and thermal expansion
17. Kepler laws
18. Moment of inertia
19. Colour coding, Wheatstone bridge, and electric devices in Current Electricity.

Probability of qualifying in JEE Advanced doesn't depend on your 10th grades in any way. So stop making such calculations and instead work hard to get enough marks in intermediate, minimum 75% is needed in intermediate in order to go for JEE. After that you need to prepare well and give your JEE Mains exam, after you qualify that you should prepare well for JEE Advanced exam, after qualifying that you're good to go. If you have got good scores then you can study in the best colleges, if not it's okay you can go for colleges which are suitable for your score. So, I recommend you prepare well, take mock tests, solve previous papers and do well in your exam. All the very best.

JEE Main is considered to be easier than JEE Advanced as it only examines the candidates based on class 11th and 12th syllabus. The questions asked in JEE Main are usually direct formula-based and easier in nature when compared to JEE Advanced. JEE Main usually tests only the speed of the candidate with 75 questions asked in the exam. JEE Mains questions can be repeated and most of these Q's can be easily solved within 2 minds each Q. JEE Advanced is considered to be more difficult than JEE Main because it included other topics than the ones from class 11th and 12th. JEE Advanced questions are concept-based and requiring in-depth knowledge of the topic. The questions are also framed using two or three concepts in one. JEE Advanced tests the speed as well as the problem-solving skills of the applicants.