If you meant UPSE, then no. You are free to chose any subject as an optional subject.

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.

So you can pick up any optional subject that you want. Either something that complements with your Graduation or something that interests you. When you are selecting an Optional subject you need to remember that the material should be easily available, you should find it interesting you and it should fetch you good marks.

Hi,

It is not like that. You need to prepare for all the subjects in UPSC Civil Services examination. The sole preparation for UPSC is understanding of syllabus. It feels you are not aware of the syllabus. For UPSC, you need to prepare for all the subjects mentioned in the syllabus. Apart from this, there will be an optional paper worth of 500 marks in which you can choose any of your desired subject and prepare as per the syllabus mentioned in syllabus. Check out the syllabus here: https://competition.careers360.com/articles/upsc-ias-syllabus