I don’t have access to real-time data or specific information about the current courses at the Indian Institute of Science (IISc) beyond my September 2021 knowledge cutoff. Therefore, I cannot provide you with accurate information about the most difficult courses or the percentage of students who fail them at IISc.

However, it’s worth noting that the difficulty of courses can vary depending on individual strengths, interests, and the program of study. Different students may find different courses challenging based on their academic background and personal aptitude. Furthermore, the percentage of students who fail a particular course can also fluctuate from year to year.

To get up-to-date and accurate information about the most difficult courses and their failure rates at IISc, I recommend reaching out to the institute directly or consulting the official IISc website. They should be able to provide you with the most current information on the courses and their academic rigor.