What are the oxidiation states of the individual elements that compose ammonium carbonate, #(NH_4)_2CO_3(s)#?
In terms of oxidation number we has...........
The weighted sum of the oxidation numbers is equal to the charge on the species, which is NEUTRAL for a salt.
The salt is unstable and decomposes (slowly) to give ammonia and ammonium bicarbonate:
Pungent ammonia gas is what gives it its original name: