Hi Katravath,

I can provide you 2016, 2017 and 2018 cutoff ranks of IIT Madras (Chemical Branch) for ST category candidates, you can get a clear idea.

In 2016, after the last round-

Closing Rank- 442

In 2017, after the last round-

Closing Rank- 386

In 2018, after the last round-

Closing Rank- 609

Therefore, you need an ST rank around 600-700 to stand any chance of getting Chemical Branch.

Hope this helps you.

All the best!!!