CBSE 12th

With 80 percentile in CAT General category, don't rush for MBA, get work ex and re-appear for CAT.

The semester fee is Rs.98000 rest depends on the amount of scholarship you get. It will be reduced based on the percentage of the scholarship.

As per the additional eligibility criteria and basis of selection, Aggregate of 60% or more marks in the qualifying examination in four subjects: English, Mathematics and any two other subjects included in List B.
Selection will be based on the rank computed from the combined weighted average of percentage scored in the entrance test and the percentage scored in the qualifying examination where the weights are: Entrance Test: 65%, Qualifying Examination: 35%.
Hence math is compulsory here so you can not apply.

The process is a little complex but don't get disheartened. Try the exam and you will make it with hard work.

For Air Force, a candidate must have passed 12th with Physics, Mathematics and English subjects. Hence you can not join Air Force wing.

After your 12th choose subjects from Bachelors of Arts, like Economics, political Science, History, Geography from any reputed organizations. It will help you in understanding the syllabus of the IAS much better than choosing Science or commerce subjects. UPSC can be written by any graduate, but by choosing B.A. In your graduation will help you better in understanding the concepts much easier compared to the other streams. Look for colleges where they provide you extra coaching for UPSC.

Minimum 60% is needed in 12th standard.

For NDA (1) 2020: The candidates possessing age between 2nd July 2001 to 1st July 2004 are eligible for the examination. If born before 2nd July 2001 and after 1st July 2004 then not eligible for NDA (1) 2020 exam. Only unmarried male candidates are eligible for NDA examination.

Yes, you can apply for the exam.
For NDA (1) 2020: The candidates possessing age between 2nd July 2001 to 1st July 2004 are eligible for the examination. If born before 2nd July 2001 and after 1st July 2004 then not eligible for NDA (1) 2020 exam. Only unmarried male candidates are eligible for NDA examination.