Some frequently chosen optional subjects in the UPSC Mains Examination include Sociology, Geography, Political Science, and History. These subjects are popular due to the availability of ample study materials, overlap with General Studies papers, and relatively achievable scoring patterns. Other subjects such as Anthropology, Public Administration, and Psychology also attract candidates. The choice often depends on personal interest, academic background, and guidance from successful aspirants. Selecting an optional subject strategically can significantly impact overall performance in the examination.