Hello aspirant,
Well, in this case that you have mentioned,
We take that extra subject only to make up one of the main subject if you have failed in one of them.
But the condition is, you should pass in physics, chemistry , mathematics and English in order to appear for jee entrance exam.

You have score also low percentage in board,
It is mandatory to score at least 75% in CBSE,
for appearing in jee mains.