Computers & IT (Non-Engg)

No, it is not possible to do M.Sc in CS after B.Sc in chemistry. You can apply for MCA if you have done your 12th with maths as a compulsory subject.

As per your degree B.Sc in computer science, you must have to do M.Sc in computer science.

This would depend a lot on your interest areas & career aspirations. However, since you have done 12th in arts you should pursue BBA. BCA (Bachelor of Computer Application) is a technical course and one would need good computer skills plus an HSC in science would be necessary to seek admission.
BCA can also be Bachelor of Commercial Arts, if you are creative in nature and have good drawing skills then you can pursue commercial arts course as well.

55% is the minimum percentage that you need in clas 12th.

Dear,
You are not eligible as:
MCA eligibility is any graduate who has passed or appearing for the final year degree examination in any discipline (science, commerce, arts, engineering or any approved university) is eligible to apply.
Candidates must have mathematics as a subject in their 10+2 course or any one year of graduation. BCA qualified candidates can also pursue MCA.
So, I would suggest you to go for MBA course.

Yes, you are eligible for doing MCA as eligibility for MCA is +2 with maths and a graduation course. You have both. So,
good luck!