Environmental Science, is an important area from which important of questions come in UPSC & State PSC, prelims and mains. If someone has done exceptionally well in Environmental Science, it is likely that his/her difference. On the other hand people have been awarded higher marks in optional, so that if someone has done exceptionally well in optional, he/she will score a lot of marks more than others. UPSC is a relative exam, only difference of marks matters.