Hi

Yes, after the completion of your BSc you can definitely write UPSC examination , this is because to be eligible for UPSC or the IAS examination there is no compulsion to be a graduate in a particular subject, all you need to be eligible is that you should be a graduate in any discipline.

You can check UPSC eligibility criteria which  is provided below :-

• You must have a bachelor's degree in any discipline from a recognised university

Minimum age limit :-  21 years

Maximum age limit :-  32 years , there's 3 year relaxation on upper age limit for obc and of 5 years for Sc/St.