B.Sc

For doing an MBA any degree will make you eligible provide you clear aptitude tests such as MAT/CAT/CMAT etc. as applicable to the institute of your study. Prior exposure to statistics, research methodology, calculus/mathematics, economics, accountancy etc. will be an added advantage while doing an MBA. MBA is multidisciplinary, any way.

B.Sc is an evergreen course.
There is a lot of scope in this field.
But, nowadays BBA is trending.
You can do BBA+MBA and then you can get a job easily.
Good luck!

No, it's not possible.
You can't do B.Sc in mathematics without having maths in 12th.

In India, there are almost no college which provides this course except this one.
IARC, (Indian Astrobiology Research Centre) in Mumbai provides one 4 months diploma course in astrobiology which is a distance learning courses.
One more thing, I would like to suggest you that do to do graduation with physics, or live sciences.
Astro-Biology is mostly a post graduate course.

Firstly, you have to clear your compartment and then think about admission.

There are many B.Sc degree courses [aided & un-aided] it's all upto your interest.
if you like IT go for B.Sc-IT, if you are a biology student do B.Sc in any biological dept but nowdays microbiology has a lot of scope but the cutoff is high so you need to check
Bio-technology also is very good
now its all upto your interest
All the best.