Yes, attendance rule is there in IIT BHU Varanasi. Students are required to maintain a minimum of 85% attendance. If anyone fails to maintain the cut-off attendance, they may have to repeat the subject as professors sometimes award Z grade to students with less than 85% attendance.
But it mostly depends on the professor of that subject. Some professor follows this rule strictly while some may don’t. So, to be safe students should maintain a minimum of 85 percent attendance. It's only for theoretically class, some professor wants 90 percent or above attendance in Lab Classes. So, the conclusion is that there is a rule of compulsory attendance (85%), but it depends on a professor.