Based on the pair of molecules, identify a structural, optical, geometric isomers, or identical. So if we take a look here at the first one, we have bonds that have spatial orientation. Usually, this is a key to giving away that we're dealing with optical isomers. Now if we imagine that this is looking into a mirror, it would see its reflection back. The H would be looking this way, which it is. The CH3 would be looking this way, which it is. We'd have our Br here. And looking in the mirror, the OH would be here in the back. So this is the mirror image of this original one here on the left. So they are optical isomers.
For the next one, we have the presence of a double bond, which usually indicates that we have a geometric isomer, but we have to check. In this one, both Cl's are on the same side, and on this one both Cl's are still on the same side. Now, they're not geometric isomers. For them to be geometric isomers, we'd have to have one where the Cl's are on different sides. Both are saying the same thing, so they represent identical molecules.
For the next one, what do we have here? So we have this structure here and we have this structure here. If we look, what do we see? We see that we have what? We have this chain here, and branching off of it is this CH3 and this OH. And then what else do we have? We have this chain here which has 4 carbons as well, and coming off of it is this CH2, and then here, O. It's better to draw it this way to show the actual connection to the O. So if you look, they both would have the same number of carbons, hydrogens, and oxygen, but they look like they're connected differently. So here we'd say that these are structural isomers. Same molecular formula but different connectivity. So this is how we classify each one of these three options.