Chemistry: For this section, the focus must be on Organic and Inorganic Chemistry. One can follow Inorganic Chemistry by NCERT, Advanced Problems in Organic Chemistry by H Pandey or Organic Chemistry by Khan Academy.
Mathematics: Mathematics is all about practice and revision. When an individual starts to practice Maths, he or she should practice a variety of sums in order to achieve expertise over the domain. In this case, one can practice from books by R.D Sharma and A Dasgupta.