Hi  1 st yr of every b tech branch you will be taught basic electronics , basic electrical ,  c language , physics , chemistry  mathematics ( differential and integral calculus) so as you have prepared for jee mains or may be any engineering entrance exam you have already covered the basics so you don't have to go and study before your btech but you can Just keep the notes of 11 12 and ncert of chemistry for reference so that you can relate the subjects better