Hello 

There are many main topics like:

permutation and combination

sequence and series

calculus

statistics

algebra

thermodynamics

fluid

optics

electric current

rotational

inorganic chemisty( main concepts)

thermo

atomic structure

equilibrium

surface chemistry

But one thing you should keepm in mind that you cannot depend upon only some of the questions because if by chance you will not able to solve those question in exam than if you study all the topics, you cancover up it in exam.

Because question can come from any topics and there is a lot of pressure and we do silly mistakes in exam so better to be in safe position ( so i would suggest you to go with full preparation and with all the concepts).

Good Luck