Which gas diffuses most rapidly when they are all at the same temperature and pressure? He, O2, NH3, H2S, or They all diffuse at the same rate at the same temperature.

He

Explanation:

From Graham's law of diffusion, lighter or less dense gas tends to diffuse faster than denser gas amongst the list, He is the lightest gas and so will diffuse faster

By definition, an atom is electrically neutral (i.e. has the same number of protons as it does electrons, plus some number of neutrons depending on the isotope). If a species were charged, it is referred to as an ion (cation for positively charged and anion for negatively charged species), also by definition.
I believe the answer is anion.