can I apply for neet 2020 if I failed in bsc 3rd year with microbiology and if yes what code should I use.

Shubham, though you have failed 3rd year, you are still a student of B.Sc. And so your code shall be 07 because code 05 is for 1st year students and 06 is for those who passed their B.Sc. But Code 07 says: Any other examination which in scope and standard (Last 02 years of 10+2 Study comprising of Physics, Chemistry and Biology/Bio-technology; which shall include practical test in these subjects) is found to be equivalent to the Intermediate Science Examination of an Indian University/Board, taking Physics, Chemistry and Biology/Biotechnology including practical tests in each of these subjects and English.