According to the guidelines, a candidate must secure minimum 50% marks (GEN), 40%marks (SC/ST/OBC), 45% marks (GEN PH) & 40% marks (SC-PH/ST-PH/OBC-PH) taken together in PCB subjects (aggregate). Your chemistry marks are not the only marks to be considered, you should have scored 40+ marks in your physics and biology papers too (if you belong to the reserved category) and 50+ if you belong to the unreserved category.