Science

Hi Tanisha,
Yes, you can pursue PG Diploma in marketing management after B.Sc (PCM). The minimum qualification criteria is graduation in any discipline. For more details, check the following link: https://www.shiksha.com/careers/marketing-manager-71

You can refer to the link for details: http://icriindia.com/

First of all you should be thorough with your B.Sc. syllabus. You should know all the basics of the subject you have chosen for B.Sc. You can achieve this by keeping contact with your teachers, seniors and reading books and the books you refer should be always reference books because the information given in the reference books is always correct and you should understand all the concepts from that reference book.
Clearing the basics is important to prepare for the entrance exam.

Go with BCA course.

It should be your decision as both the fields will give you good respect. If you become a doctor, you will definitely earn more than a teacher.

No doubt, MCA is better than M.Sc. M.Sc is for 2 years while MCA is for 3 years. As both are technical courses so 1 year extra is advantage and company in placement prefer MCA candidate over M.Sc candidate. But if you have good skills and good knowledge about your subjects which you have studied in graduation, then you can go for M.Sc.