Hello,

There are certain important factors to be taken into consideration prior to deciding for the optional subject in UPSCA, first is obviously your interest in the subject, secondly it's important to go through the syllabus, how long will it take to complete, availability of study materials too matter in this, for instance last year an engineering graduate who was topper from IIT chose to go with physics as optional subject, so you can go ahead with chemistry as you mentioned, else if you like maths, you can have it as optional too, and it's quite a good scoring subject as well, see what happens if you choose a subject as optional that you're already well acquainted with then you don't have to start afresh and put in more efforts, that's why majority of people chose to go with their graduation subject because the syllabus of optional subjects in UPSC is equivalent to that of graduation level only, however there are certain candidate who take a different route like they come from engineering background but have taken up philosophy, public administration to name a few as optional, so it basically depends on your interest, go through the syllabus, previous year papers to get an idea, and as I said availability of study materials is too important criteria.