Sudhanshu, the cutoff of PRMO varies every year and it also differs from state to state. Upto 300 students from class 8 to 11 and about 60 students from class 12 are selected for the next round from each state/ region. Please mention your region so that I can answer you specifically.

Otherwise you can also go through the past years' cutoff for each region for PRMO (2019 and 2018) from the given link: https://school.careers360.com/articles/prmo-result/amp

For your reference, the highest cutoff marks for classes 8 to 11 was 38 for Andhra Pradesh followed by 28 from Telangana whereas the cutoff for Manipur, Meghalaya, Nagaland and Tripura was 2 marks. Hope it helps.