The optional subjects available in the UPSC Mains Examination include a diverse range of fields. Some common choices are Anthropology, Geography, Political Science, and Public Administration. Other subjects include Sociology, History, Literature in various languages, and Law. The selection of an optional subject should be based on individual interests, strengths, and the availability of resources. Proper understanding of these subjects contributes immensely to overall performance in the Mains Examination, alongside the general studies papers.