Is it necessary to score 50% marks in bachelor degree if I want to apply for MBA

U may need to outperform in WAT GDPI in the admission selection processes, if u are aiming at top B schools.
Usually there is a weight age given to your grad scores, but I believe not many B schools have a clear cut criteria that a candidate must score above 50%, all that they have is the candidate must pass.
Aim for good B schools, do all the MBA entrance exams well. Almost 50 % weight age will go to the entrance exam scores and they decide whether u get a call from a B school or not.
All d best :)