Which defines what element the atom is? a. protons b. neutrons or d. electrons. I think it might be neutrons, but can you verify this?

The element of an atom is defined by the number of protons it contains. Therefore, the correct answer is the option a) protons. To verify this, you can use the periodic table. The periodic table lists all known elements, and each element is represented by its atomic number, which corresponds to the number of protons in the nucleus of an atom of that element.