Hello,

Are you asking this question in the context of physics and chemistry as optional subjects in UPSC, then optional subjects have syllabus equivalent to that of graduation level studies, it's always best to go for graduation subjects as optional since you will already be acquainted with the subject, to know the exact details about the important topics in the respective subjects, go through previous year paper at https://www.upsc.gov.in/examinations/previous-question-papers