In the UPSC Mains exam, the qualifying paper is the Indian Language paper and the English language paper. These papers are designed to test the basic proficiency in the respective languages. Candidates must score a minimum of 25% in each of these qualifying papers to be evaluated for other papers in the Mains. It's important to note that while these papers are qualifying in nature, they still require thorough preparation. Candidates should practice writing and comprehension skills adequately to meet these requirements effectively.