The optional subjects available for the UPSC Mains are diverse, covering disciplines like Anthropology, Geography, History, Political Science, and Public Administration, among others. Candidates can choose one based on their interests, academic background, and comfort level with the subject. The selected optional subject allows deeper exploration of the material and contributes significantly to the overall score in the Mains examination. It’s advisable to choose a subject with adequate resources and previous years' question papers for effective preparation.