Hello

List of important topics /concepts /chapters for your JEE mains having the highest weightage in examination previous year trends is given below subjectwise :-

PHYSICS

*Modern Physics -20 marks
*Heat and Thermodynamics-12 marks
*Optics - 12 marks
*Current Electricity- 12 marks
*Electrostatics- 12 marks
*Magnetics- 8 marks

CHEMISTRY

*Transition Elements and Coordination *Chemistry- 12 marks
*Periodic table and Representative Elements- 12 marks
*Thermodynamics And Gaseous State- 8 marks
*Atomic Structure- 8 marks
*Chemical Bonding - 8 marks
*Chemical And Ionic Equilibrium - 8 marks
*Solid State And Surface Chemistry - 8 marks
*Nuclear Chemistry And Environment - 8 marks

MATHEMATICS

*Coordinate Geometry-20 marks
*Limits, Continuity and Differentiability-12 marks
*Integral Calculus:- 12 marks
*Complex numbers and Quadratic Equation :- 8 marks
*Matrices and Determinants:- 8 marks
*Statistics and Probability:- 8 marks
*Three Dimensional Geometry:- 8 marks
Vector Algebra:- 8 marks

You should focus more on above topics as time   left for jee mains 2020 preparation is less  and they carry the highest weight age in exam

You can get chapterwise weightage for all the chapters for each of physics Chemistry and Maths by going through

https://engineering.careers360.com/articles/jee-main-syllabus-weightage

Thankyou