dear sir, i am a commerce graduate, specializing in accountancy, i would like to know which are the most scoring subjects for csat(upsc) and which optional subjects should i take up.

Dear Naina, CSAT generally is not based on some specific subject. It is a mix up of objective type general knowledge questions on several general topics, as you can see from the syllabus, which you can download from the following site of the UPSC: http://www.upsc.gov.in/exams/misc/csp2011-syll.pdf