CBSE 12th

Hard work, self-study and practice should be your 3 mantras to score 95% or above in class 12th.
Good luck!

IITs are the best institutes for engineering in India. You must target IIT-JEE Mains/Advanced. Apart from IITs, NITs are the next best. NIT-Jaipur, Warangal, Trichy, Bhopal, Surat are some of the best. Among private institutes, VIT-Vellore, BITS-Pilani/Mesra are reputed ones. Other government institutes are IIST-Trivandrum, IISER Bhopal/Pune/Bhubaneswar.

There are very few colleges offering 100% placement and they include:
IIM, Indore
Nirma University, Ahmadabad
There aren't any more credible institutes for this course. And, anyway it does not matter. If you do integrated BBA and MBA, it will take 5-years and the course fee will be very high and instead if you do 3-years BBA or BMS from a good state university affiliated colleges such as St Xavier's, KJ Somaiya, NM in Mumbai that will cost hardly 1 Lac including everything.Further, you will have more options for MBA later.

I think your question is wrong you 140 cut off marks in entrance exam, by the way I will give a link that will help you to find the college according to your rank:
https://www.resonance.ac.in/reso/news/JEE-Main-Branch-Predictor.aspx

Definitely B.Tech is better than B.Sc because it has good scope than B.Sc, if you go for B.Sc you'll get low salary and you can go for research but if you go for B.Tech, you can go for anything you need and you'll get a good salary.
choose wisely.

It depends now on your biology degree which you hold. If you want to go by trend, I suggest that you should proceed with nutritional sciences for clinical aspect or microbiology or biochemistry for non-clinical aspect and it shall suffice your desire, but it all depends on your present qualification status.

You can do full-time Diploma in Engineering along with class 12th board in private mode. It will require extra effort and if you have the will to do both simultaneously without impacting your academic performance in both the courses, you may go ahead.

See in CBSE, since before, NCERT numerical problems are always tweaked to make it simpler or difficult, but the main aim is to make everyone score 52+ out 70 in theory so numerical problems are in average count usually. So in physics, 40% are numerical requiring least derivations 20-30% need a bit of derivation ideology too & lots in chemistry are simple NCERT modified ones that also not to a great extent. Still, check the sample papers issued by CBSE just before exams. Many problems turn common with slight modifications.

Hello Harshita,
12th from NIOS is considered as equivalent to any other 12th. Hence you would normally be qualified to join degree course for journalism. Of course assuming you fulfil other eligibility criterias if any.