Candidates have various optional subjects available in the UPSC mains examination, allowing them to choose based on their interests and background. Some popular optional subjects include Geography, Public Administration, Political Science, History, and Sociology. Each subject offers a different perspective and depth of content, catering to a wide range of aspirants. The selection of an optional subject is crucial, as it can significantly impact their performance in the Mains examination and ultimately influence their overall ranking in the UPSC selection process.