if I want to do B.sc agri then which exam preferred and college

You can get direct admission in B.sc in Agriculture Course after Completing 12th standard . But in some cases the Institution may conduct own Entrance Examination , Based on the Entrance Examination performance , the Institution may give admission for B.sc in Agriculture Course .

Here are some good colleges for B.Sc Agriculture you can prefer.

Government Barjindra College

Tamil Nadu Agricultural University

Metas Adventist College

Punjab Agricultural University

College of Veterinary and Animal Sciences