practice problem

This is an example problem from AP Chemistry practice exam about Isomers. Isomers are compounds that have the same elements but different connectivity. The answer to this particular problem is answer choice C. Both compounds have 2 carbon, 6 hydrogen, and 1 oxygen. To solve the problem you need to quickly identify the different elements in the compound and count them. That would need to occur for each of the options until you come across an equal amount of atoms.