See in general, if one have 50% marks in the TIFR GS examination, then its quite confirmed that the student will get a call for the interview. Now every year, the difficulty of the paper change for different subjects and as a result, the cutoff changes. So nothing for sure can't be provided, although you have moderate chances to get the interview call.

To know more about TIFR, visit the link below:

https://www.careers360.com/university/tata-institute-of-fundamental-research-mumbai

I hope this answer helps. All the very best for your future endeavors!