Hello there,
You haven't mentioned the name of the examination you are enquiring about. If you are asking about JEE Main, then for 80 percentile, the All India Rank will be 173802 approximately. Now, it is difficult to say the marks as the 'marks vs percentile' changes every year depending on the difficulty of the question paper, and the performance of the other candidates. Still, the marks will be in the range of 90-100 approximately.
Hope this answer helps you.
Thank you!!