Hello aspirant.. Norms for Admission in B.A psychology is different for different institutes. Admission Screening vary from College to College.Some Colleges/ Universities involves merit base selection procedure such as Ambedkar University while some Colleges/Universities such as Banaras Hindu University, Jamia Milia Islamia, Lovely Professional University, etc, demand for entrance exam. So admission procedure will totally depend on the Institute you apply. You need to score really good in class 12. Universities like DU see the best three or best four percentage of Higher Secondary. 

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