Can I score 150 marks in jee mains by studying only 12 th cbse portion ?

Mostly the syllabus is based on Class 11th & 12th  for IIT JEE entrance exam but completing your 11th & 12th syllabus can help you to build your basic concepts. To get a good score you need to refer the other books given below:

Physics -Concepts of Physics by H.C. Verma, Principles of Physics by Resnick and Halliday, Problems in general Physics by I.E. Irodov.

Chemistry- Organic Chemistry by Paula Bruice, Advanced Problems in Organic Chemistry by MS Chauhan, Concise Inorganic Chemistry for JEE Main and Advanced by JD Lee, Physical Chemistry for Competitions by O.P. Tandon,

Mathematics- IIT Mathematics by ML Khanna, Coordinate Geometry for IIT JEE by SK Goyal, Objective Mathematics by RD Sharma, Higher Algebra by Hall and Knight.

Here are some preparation tips you can follow:

Build and Focus on your strengths
Check your short Notes & Revise the important formulae:
Don't go on doing Mock Tests
Dont let self -doubt creep in
Gets sufficient practice and revision
Try to solve at least 70-80 numerical every day.
Do read, errors and measurement, environmental chemistry, and sets, relations.
Read the questions first and mark which would ypu do first. This will definitely avoid wastage of time on other questions.

Good Luck!