B.Sc

The link below gives you the list of B.Sc colleges in Delhi/NCR:
https://www.shiksha.com/science/colleges/b-sc-colleges-Delhi-ncr

Yes, you can. The eligibility for IIT JAM is to have a minimum of 55 percent (for general category) in Bachelor's degree and 50 percent (for reserved categories). For more details, you may refer the link below:
https://www.shiksha.com/science/iit-jam-exam

The minimum eligibility for engineering and B.Sc is to have scored at least 50 percent in your board exams. There might be a 5 percent relaxation for reserved category students. However, the eligibility varies for each college and you may also need to clear an entrance exam depending on the colleges in which you wish to get admission.

No,
You cannot take admission for M.Tech after completing B.Sc.

Hello,
https://www.shiksha.com/mba/articles/top-5-mba-specializations-in-india-blogId-3223 Visiting the given link would help you get some valuable information about the MBA specialization you would wish to pursue.

As for my perspective, you should go for B.Sc or B.Tech in private college, because your class 12th percentage are not good.

Actually, going for MBA after Science or Technological background makes more sense if you take specializations like Data Science, Operations, and Business Analytics. As research work in Bio-Tech is taking big strides I guess analytics along with Bio-Tech will be a good mix. Many firms in pharmaceuticals and food-processing industry need quality analysts. So, if you get opportunity to get Data Science/ Business Analytics course, then its a hood option.