CBSE 12th

Four months are more than enough for JEE Mains paper provided you are clear with the class 11th and 12th concepts. So, you need to just brush up what you have already studied. Don't go in for extra efforts or extra books at this 11th hour. Focus on self studies and try to remember the formulas and just solve the past JEE papers and MCQs more and more.

Go for MBA in SMU or IGNOU.

You can go for graduate/Diploma/certificate course according to your ability/choice. Go for a reputed institution.
All the best.

There is no option of BBA+ MBA integration after 12th board. It just offers a liberal studies and in 3rd year you have an option of choosing your major and minors according to your choice . The course is for 4 years.

Hi Devraj,
Firstly, you will have to pursue graduation in chemistry i.e. B.Sc chemistry (honors) from any of the reputed universities including Delhi University colleges. You can pursue your Masters from IITs by clearing IIT-JAM. There are other institutes as well like Tata Institute of Fundamental Research, Indian Institute of Science, National Institute of Science, Education and Research, Bhubaneswar.
All the very best for your future endeavors.

Please refer to the link provided below for a list of colleges from Mumbai which offer courses in Microbiology(B.Sc). You can download their brochure which contains important information like course eligibility, admission criteria, placement records, rankings and reviews etc.
https://www.shiksha.com/science/colleges/b-sc-microbiology-colleges-maharashtra

Hi,
Delhi University conducts the Joint Admission Test (DU JAT) in the month of June. The exam is a gateway for admission to 6 colleges that offer Bachelor of Management Studies (BMS) and 8 colleges that offer BBA (FIA) programs and Business Economics.
Try can get more than 95 percentile.