Hey Shuva

I would like to tell you that please dont choose your optional subjects by the list of the subjects that is taken by maximum candidates but on the basis of what subjects you like and want to persue. Be it history, polity, sociology or anything else the only thing that matters is how good you can be at that subject.

However over the years the subjects which have been chosen as optional by most students were psychology, literature(native language), zoology, anthropology, mathematics etc (depending on the stream you are from).

There are a few things you need to keep in mind while choosing your optional subject:

If the study material for that subject is available

If that subject will get you good scores

Your interest, aptitude and capacity

Time you need to study that subject

If the syllabus of that subject is overlapping other subjects taken by you.