Krish, to b e eligible for UPSC, you should have completed your Graduation in any stream. So you can study your Bachelor's in any stream. But previous years Statistics state that Candidates who have studied History, Anthropology, Geography have been able to score good than their counterparts. So you may try that too. This way when you take an Optional subject for your Mains, it would be helpful for you.

UPSC is a 3 stage   selection process involving Prelims, Mains and Interview which tests your personality test. Prelims has 2 Papers namely General Studies and CSAT.

General Studies has Current Events, History of India and Indian National Movement, Indian and World Geography, Indian Polity and Governance, Economic and Social Development, Environmental Ecology, Biodiversity and Climate Change and General Science.

CSAT has Comprehension, Interpersonal skills including communication skills, Logical Reasoning and Analytical ability, Decision making and problem solving, General Mental Ability, Basic numeracy and Data Interpretation.

Hello

You can choose any subject  of your choice based on your interest for your graduation.

This is because,

to be eligible for UPSC or the IAS examination there is no compulsion to be a graduate in a particular subject, all you need to be eligible is that you should be a graduate in any discipline

So you can choose any stream of your interest, but yes if you are interested in Arts then

choosing Arts or the humanities can be really helpful for your UPSC  examination, this is because in Arts you will be learning subjects like history , polity etc which are a part of the UPSC syllabus so it will help you in your upsc examination.

Thankyou