Which biphenyl is optically active? Which biphenyl is optically active?


I know that it can never be 1. I don't think it will be 4 either as I read that it should be ortho-substituted biphenyl.
So, when I look at 2 and 3, I can't make out which one should be the correct answer.
Should it always be two ortho substituents on each phenyl group for it to be optically active?
Also, what if the two groups on the same phenyl are different, will it always be optically active in that case?
(3) is not chiral, so maybe it is (2).