[Cassowary]

The question is this: which one of these is an optical isomer?

1.
2.
3.
4.
5.
6.

2, 3, and 4 are out because none of those have a central atom with 4 different groups on them. 5 is out because it's an aromatic molecule and its groups are going to be on the same plane so it'll be "flippable". That left 1 and 6, and I looked 6 up and it didn't have an optical isomer, which leaves 1, but however I draw that I get something that can rotate back over itself.

So, yes, I'm very confused and wondering if I missed anything.

[UG]

5 is out because it's an aromatic molecule and its groups are going to be on the same plane so it'll be "flippable".

Oh I don't know about this, try and see if you can build this model by hand (if you have the equipment). You will find that it isn't an aromatic molecule/not flat (unless you forgot to draw the double bonds)