in this example question. It says which of the following compounds would have an oxidation number, or oxidation state equal to zero? So remember when an Element or Adam is found in its standard or natural state, it's oxidation number or oxidation. State is equal to zero. So if we take a look here, we have sodium to begin with. A any remember exists as a mono atomic element in nature. It's natural form is just n a. So this would not be equal to zero. Next we have chlorine. Chlorine exists as a die atomic molecule. Exists naturally. SCL, too. So this is a helium, one of our noble gasses. All the noble gasses art, mono, atomic, meaning they exist by themselves in nature. So this is the natural state of helium, and therefore it's oxidation number or oxidation. State would be equal to zero. So this is our answer. But let's look at the last one. The last one is mag unease, and they're saying it's four. Mag unease is one of many elements that exists as mono atomic elements in nature. So it's natural state is just mn, so this would not work so out of all the choices, only Option C would have an oxidation number of zero