Studying 12th standard. Science stream.

I want to study BA Economics

You are from science stream and have interest in BA economics. For this you can apply in various universities and institutions like DU, Shri Guru Gobind Singh College of commerce, Presidency college, MCC college etc for BA eco course. In some colleges there can be entrance and in others based on merit. Mostly it will be entrance based. The course is good and if you want you can choose to do Eco hons which will be a more intensive course in economics.
Let me know if you have any other doubt.