Hi Kaustubh,

Merit-Based admissions at the University of Delhi is wherein you will be calculation an Average of you best four subjects according to which you will make the merit list of a particular course and college. Best of four is wherein an average of your best four subjects is taken. In your case since you are interested in the science stream, your best of four subjects will be English, Physics, Chemistry Biology/Mathematics depending on the subject you wish to pursue. To know more about the best of four system please refer to the link given below.

Link: Best of Four Calculation