Answer to this question depends a lot on your interest and long term career goals. You've not specified what have you pursued at graduation level.

Job prospects and interest for a certain area of study goes hand in hand, after all you just don't want to slog all day and not find your career choice  interesting enough to keep going further.

Opportunities are present in all the field you have mentioned, let me analyze this individually-

Job prospects for MSc Chemistry is  teaching in colleges, or schools, Chemical companies, Pharmaceutical companies, Government and private research organisation, in Central government departments and in companies like SAIL , ONGC, etc.

Job prospects for MSc Polymer Chemistry lies in wind Energy Sector, Energy Industries, Chemical Manufacturing Companies, Pharmaceutical companies, Automotive Companies, Defence

Job prospects for MSc Computer Science lies in

After completing M.Sc in Computer Science, there's career opportunities in government sector organisations like National Buildings Construction Corporation Limited, Centre for Development of Advanced Computing (C-DAC) and Bharat Sanchar Nigam Limited (BSNL). Project Executive, Junior Executive and Telecom Technical Assistant. various hardware and software companies like Intel, Infosys, Tata Consultancy Services, Accenture, Dell, HCL,in various database and mobile companies, many web designing companies like Advanced Studios, Agency Net Interactive etc. as Web DeveloperASP.NET Programmer, PHP Programmer, Web Designer etc

For MCA, one can work as software consultant, software application architect, system analyst, business analyst, app developer.