I have only 50 percentile in JEE Mains. Should I take a part in counseling or should I take a drop?

You are eligible to take part in counselling, or if you have a drop year then you can opt for that also. Whatever you opt, best wishes from my side.

You can take part in counselling and look for an option that suits you. I would only suggest to take a drop if you are willing to work hard for a year to improve your rank.