CBSE 12th

After 12th with science, you need to pursue a Bachelors in your field like BE or B.Tech or equivalent degree. Only then you can apply for MBA.

Yes, there is. All you have to do is check out the HRD ministry website or visit the HRD department. Certain states like MP and Rajasthan offer really good scholarships for students who get selected in IIM or IIT, regardless of their percentage.
All the best.

You can do CA, CS, Law, Management, MBA, BBA, or many more.

For admissions at NIT Patna, candidates should have secured at least 75% marks in class 12th exam or be in the top 20 percentile in the class 12th exam conducted by the respective board. For SC/ST candidates, the eligibility criteria is 65% marks in class XII.

No need of maths in+2 for B.Com.

Please refer to the article mentioned at the link provided below to gauge the cut off trends for DU colleges for the past few years. 90% is a good percentage, however, the first cutoffs for some of the top colleges in DU touch 99-100% so you might have to wait for successive cut off lists. Please read more at the article mentioned below.
https://www.shiksha.com/humanities-social-sciences/articles/du-cut-off-trends-for-past-years-blogId-12697

Hi Shubham, as every year the cutoff increases it is difficult to get a call at this percentile. But it's all relative, so be prepared for the interviews. Also, CAT score has the maximum weightage of 75% for getting a call and 60% in the final selection. The interview has 20% weight in the final selection.