Hey,

Yes you are eligible to sit for thr NDA exam but as you have only biology so you can only apply for army and not for other branches.

In order to be eligible for naval as well as air forces a candidate needs to have physics and mathematics but as you not have maths so you can only apply for army.

Below I have attached a link that contains detailed information in the exam pattern as well as it's eligibility.

https://competition.careers360.com/articles/nda-eligibility-criteria

Hope that helps.

Thank you.