Hi Swaroop,

Yes you can take psychology after 12th with science.And cut off  totally depends on from  which category belongs as if you belogs from general 97%+ is required for top colleges in DU.

For OBC it is 94%+.

For SC it is 90%+

And for ST it is 88%.

For PWD it is 85%.

Hope this will help,Please feel free to ask if you have any other queries.

Thank You.