Hi Aditya,

Hope you are all fine. With reference to your question, if you have passed your 12th with PCM (Physics-Chemistry-Mathematics) from Bihar Board and you want to give biology exam as a single subject from NIOS, your Bihar Board 12th marksheet will not lose its validity

However, if you are planning this to write your NEET, do note that at the time of document verification certain colleges might not accept it.

Hope this helps.