hello there
since you are Btech and mtech students so you are not eligible for ugc net .however you are eligible for csir net .and you have to appear in csir net exam .you can chose any subject from the list of subjects provided by the official website .try checking the eligibility criteria and subject options
https://csirnet.nta.nic.in/webinfo/public/home.aspx
Admit Card | Eligibility | Application | Preparation Tips | Result | Answer Key | Cutoff
Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile