Hello

It would be difficult to tell you about the exact marks required for admission into IIST as the cutoff required for admission varies every year. Factors determining the cutoff are:

Number of seats available
Number of candidates appeared for JEE Advanced 2020
Number of candidates applied for IIST B.Tech admission 2020
JEE Advanced 2020 difficulty level
Previous years’ cutoff trends

You can go through the link below and check the previous year cutoff for reference

https://engineering.careers360.com/articles/iist-btech-cutoff

Good Luck!