Science

Go for microbiology as it will give you more options in future when you start searching for jobs. Biotechnology will narrow down your future path and it will be difficult to get good job after post graduation. While microbiology gives you wider prospects in especially government jobs.

Go through the link below for complete details on NTSE exam:
https://www.shiksha.com/exams/ntse

Eligible for what? Please specify clearly so that I can guide you further.

Although it depends on the college/university, but yes, there is an entrance exam for these courses.

Hi,
Please mention the college/university where you wish to take admission.

A few good colleges offering M.Sc. Zoology are:
1) Ramjas College, Delhi
2 )HansRaj College, Delhi
3) Christ University, Bengaluru
4) Loyola College, Chennai
5) Miranda House, Delhi
Kindly check individual college's website for their entrance exam procedure.

For doing architecture you need complete your 12th in science and give an entrance exam.

Refer this link for the eligibility criteria of NEST https://www.shiksha.com/college/national-institute-of-science-education-and-research/nest-exam.