Hello,

When it comes to choosing optional, the best thing is to go for the subject of your graduation because of two reasons, first the syllabus of optional in UPSC is nothing short of graduation level, and secondly, you'll be acquainted with the syllabus already, so there will be less of a burden, and you don't have to worry about choosing Accountancy and Commerce as a subject, many people with Mathematics as optional too have qualified, so there's no problem as such, just go through previous year paper, solve mock tests on a daily basis, this too should be followed firmly.