Dear aspirant, 

MBA is a post-graduate course hence in order to pursue it you must be under-graduated. You cannot give that after 12th. First do your bachelors in any stream yoh want.

12th scores are considered while calculating the total marks. As you are of science stream if your score is 90 or above then you will get maximum 10 points. If you have less than 50 then you will get min 1 marks. 

Hole this helps. All the best..!!