Manish, If you are studying  Physics and Chemistry already in your 12th, you can take up Biology as an additional subject from NIOS. You will need a minimum aggregate of 50% in Physics, Chemistry and Biology combined. It is 50% for General Category, 45% for PWD and 40% for OBC,SC,ST. Now regarding the application form, for 2021, you will mention your regular 12th board details like Roll number, School, etc. Because that is from where you are studying your 12th. You can submit your Biology marks separately.