which reference book should i buy to score good marks in phy?

for you study you follow  only and only N.C.E.R.T text book,  which is very  good book, and if  you  go through it  i am very sure  you shall at least get very good rank in AIEEE, now for the further study, i advise you to follow

University Physics by Sears and Zeemansky. Pearson edition\

 University Physics by Resnick, Halliday and Walker. these both  books are very good  for concept building

Now H.C verma's Physics part  1 and Part 2 is very good   for mastering in numerical problems.