What 's the difference between some of which, some of them or some of those?

Theorists realized that physics led to a plethora of new phenomena, ............. defy common sense.

1. some of which   2.some of them  3. some of those

The correct answer is 1. but why 2 and 3 is incorrect?

Is "which some of them" exactly equal to "some of which"?

Thanks.