BCA

Definitely biotechnology, the field is comparatively new and better than BCA, these days every Tom, Dick and Harry is either an Engineer or BCA certified, do something that is unique and creates a demand for you in new market.

Surely you can, but depends on the subjects you have had in your higher classes. If you are from a science background with maths or even commerce with maths you can apply for a BCA degree in Patna University.

Indian IT industry is in slow decline phase because of outcry against outsourcing in Western countries and increasing restrictions on working visas. Jobs are difficult to get if you miss campus placement. You will face lots of challenges to get job after BCA distance learning as there is no facility for campus placement for students who complete graduation or Post graduation by distance learning.

Both are best but its depend on you that what you take interest on B.Tech or BCA.

If you are looking for job prospect then after BCA you can work as a software developer, web developer, graphic Designer, App Developer for different platforms, system management, DBMS, Networking.
Various reputed companies like Wipro, Accenture, IBM, TCS, etc. recruits the BCA graduates who continue their higher studies in the field of Computer and software field.
You can also start your career as a junior programmer in various IT firms.

All Bachelor degrees have some value in there field we can not say that this degree have scope. The thing is that every degree have there own scope with different features. So, do any course but be perfect in that.

I think it's quite a decent percentage. So, you should start focusing on your graduation right now rather than thinking about your 12th.

Placements are good in reputed government colleges like NIT or IIT, also some other government aided institutes also have nice placements, and some great private universities also render great placements such as BITS or VIT.