i am a STD 10 student , which course to choose after 10 to be an ethical hacker

Make sure that you understand the field of ethical hacking. and If you are confirmed that you want to do it then take Computer Science as a subject in 11 and 12. You will get to know the Basics of computer from there and also you will learn a programming language which is not necessary but very helpful in ethical hacking.

It depends on your Board, what programming language you are going to learn. If you are from CBSE then you might get option of C++ or Python. And if you from ICSE Board then you might study Java or Core Java.

But any programming language will help. At least you will understand that how a program is created or how it works. These skills are necessary if you want to do Reverse Engineering stuff( part of ethical hacking). You don't have to think much if you are in 10th class. But after 12th make sure that you do something related to computer or cyber security. Until then no need to worry.
Focus on you 11 and 12th studies as well. They are really important to set a good foundations in any field in future.

Feel free to ask if you have any more queries.

All the best!