Hii swaroop,

Regarding the ST category 50 Marks in GATE is a good score but you won't get a PSU with that score.You can do your masters in good NIT.Getting a seat in IIT is also possible and have a chance of getting it .However the final selection depends on the GATE score,difficuktt of the exam thereby the CUT off is declared by the officials.As the cut off is not yet released wait for the result.You may a IIT but getting a PSU is low chances.If you can score between 65-75 marks,PSU will be an easy task for you.

All the Best....,