Put your hands on top of each other. They can't be superimposed.
1 and 4
2 and 3
are the enantiomers. This is because they are exact mirror images of each other. The bonds (dashed / wedged) are opposite, this is a very simplistic way of looking at it until you learn R/S configs.
I noticed these questions are from the RSC Olympiad. I have an RSC Membership (I think you can make a free account that just gives access to these resources) and so I am more than happy to send you the mark schemes if you feel like they would productively benefit your work.