Hello Nithesh AS!

Yes, you can apply for NDA exam while you are studying commerce in class 12th, but you will only be eligible for the army as the other two services give you a b.tech degree for which science stream is compulsory in class 11 & 12. But the following conditions should also be kept in mind:
1) Your age must be between 16.5 and 19.5 on the day of reporting to the academy, provided you make it in the final merit list and get the joining letter.

2) You must be able to provide the class 12th marksheet and certificate on the day of reporting to the academy, or before the cutoff date as stipulated by the respective HQ.

All the best!