M.Sc

MBA is the right combination for you as you can learn the aspects of management also.

There is no entrance exam in Loyola for M.Sc in mathematics.

If you have a deep desire to become a mechanical engineer and have maths as one of three optional in your B.Sc then you can do 3 year B.Tech in mechanical engineering or M.Sc in electronics or MCA.

It is not feasible and also may not be allowed by the universities.

MCA will be better option. In MCA, you will get more practical knowledge in comparison to M.Sc, as it's based on theory. Now most of the IT firm demands for MCA candidates.

Most of the colleges have eligibility criteria of relevant stream. So, do check eligibility criteria before opting M.Sc Biotech. Mathematics is not a big issue in this.

It depends on your choice and interest. Biotechnology is a research oriented field, where you have to work hard. Those who are keen to gain knowledge and love to serve society by the mode of research can opt biotechnology. Although, every stream is good unless we have interest in it.

You should go for M.Sc in microbiology. It will be a better option for you in all prospects.