The marking scheme for the optional subject papers in the UPSC mains consists of a total of 500 marks (250 marks for each of the two papers). Each optional subject is designed to test the candidate's depth of knowledge and understanding of the subject matter. Candidates can choose from a variety of subjects for their optional papers, which can influence their overall ranking. There is also the integration of negative marking for incorrect answers in the preliminary exam, but the mains exam does not have negative marking. Scoring well in the optional papers can significantly impact the final outcome of a candidate's examination process.