M.Sc Eligibility

You can complete B.sc in a college who has permission to provide you an authenticate graduate certificate. after that, you can apply in Australia.

Yes, you can. Your studies must be aligned with your career plans and you must know yourself why you want a MS now. Further you must take GRE and TOEFL for meeting the eligibility criteria. I will also suggest you email the universities before applying.

Dear Poonam, three years degree from India is accepted in UK and Ireland, so you can apply. However check for minimum percentage requirements as top schools such as LSE requires a minimum of 70%. Additionally you need to take IELTS or TOEFL.
Best Wishes

Yes, you can apply for Masters in Economics in the UK and Ireland. Have a look at Masters in Economics offered by Trinity Collge Dublin and University College Dublin in Ireland, and University College London and The University of Manchester in the UK. However please be aware that it may be difficult to find a job in the UK with the removal of post study work option. Also the European economy though improving, it may be difficult to land a job in Ireland.