what qualification code should be filled in 2020? i have passed class 12th in 2016 and in b.sc nursing 4th year?

Nikhil, your code will be 02. Because though you are in your B.Sc final year, it doesn't have Physics, Chemistry and Biology as your subjects and the highest qualification in which you have studied these subjects is your 12th and so the code will be 02.

Code 02 says: The Higher/Senior Secondary Examination or the Indian School Certificate Examination which is equivalent to 10+2 Higher/Senior Secondary Examination after a period of 12 years study, the last two years of such study comprising of Physics, Chemistry, Biology/Bio-technology (which shall include practical tests in these subjects) and Mathematics or any other elective subject with English at a level not less than the core course for English as prescribed by the National Council of Educational Research and Training after introduction of the 10+2+3 educational structure as recommended by the National Committee on Education.