The mark scheme says that only A is a hydrocarbon... why aren't they all? It also says B isn't an ether group, but surely it is because of the oxygen atom on the end?
A hydrocarbon only contains hydrogen and carbon so the other two aren't hydrocarbons because they also contain oxygen. B is an aldehyde not an ether because it has a HC=O group on the end. An ether must have an oxygen singly bonded to 2 carbons.
The mark scheme says that only A is a hydrocarbon... why aren't they all? It also says B isn't an ether group, but surely it is because of the oxygen atom on the end?
A hydrocarbon is a molecule which contains only atoms of hydrogen and carbon. Molecules B and C contain oxygen atoms as well as hydrogen and carbon atoms, and thus are not hydrocarbons.
An ether group is R-O-R', like the one in 5-membered ring in molecule C. B is not an ether group, as it is only connected to 1 carbon atom via a C=O bond. This molecule is actually an aldehyde.