Which of the following does not represent the possible structure of an acid? So remember, we said that generally speaking, when it comes to an acid, it's a covalent compound that has the hydrogen ion located at the beginning of the compound. The exception to this is acetic acid. If we take a look here, this is covalent with the hydrogen in the beginning, and that's because it's hydrobromic acid. Here we have a covalent compound with hydrogen in the beginning, so here this is iodic acid, and over here we have hypochlorous acid, covalent compound with a hydrogen in the beginning.

The answer is c. This is CH₄, also known as methane. It is not an acid. The hydrogen is not found in the beginning of this covalent compound, and by the definition we used earlier, it would not be classified as an acid. Now, there are other technicalities that make it not an acid, but just go by that simple definition.