Hello STudent, The new revised rules of Bihar School Education Board is if any student fail in compulsory subject and get high marks in additional subject then the additional subjects marks will be counted. The candidates will   able to appear in the board 10th class examination to get an average pass mark.

Regarding yourself it may be said that if you get less marks and fail in biology and get high marks in your additional subject then additional subjects marks will be treated and counted for it and you will be able to get pass marks in average

Hope this helps.