I secured 83% in icse 10 can i score above 90% in science in cbse 12 give tips to become topper ?

By dreaming of becoming topper you will never top. Devote your time to study and nothing else. Read NCERT thoroughly. I scored 80% in ICSE(2009) and now 75% in ISC(2011). I worked quite hard but still could not score more than 80. So I advise you to concentrate on studies only and stop dreaming of topping.