Hello,

As long as a candidate possess strong hold on mathematics, it's definitely a good option and scoring subject, unlike say in case of general studies papers mathematics as a subject require consistent practice, it's also a static subject, the questions asked in the exam are subjective by nature, it's repeated as well, so going through previous year paper helps a lot regarding this, for example a maths graduate or say an engineering graduate will find it comparatively easier to have maths as optional since they have studied the subject at graduation level unlike say some one who have studied it till 10th or 12th standard, although there is no restrictions in having any subject as optional in upsc, but what happens say in if you choose subject which was not part of your graduation studies, you will be required to put in extra efforts as you have to start afresh, it's also not always that a person will always go for graduation level subjects as optional, there are exceptions, choosing an optional depends on various factors such as primarily your interest in the subject, how vast is the syllabus especially if you haven't studies the subject at graduation level, what about the availability of study materials etc, so these are important factors prior to deciding whicch subject to go for optional.