Here's why:

* Ammonium ion (NH₄⁺): The ammonium ion has a +1 charge because nitrogen has a +1 oxidation state and each hydrogen has a +1 oxidation state.

* Nitrate ion (NO₃⁻): The nitrate ion has a -1 charge because nitrogen has a +5 oxidation state and each oxygen has a -2 oxidation state.

Since the charges of the ammonium and nitrate ions cancel each other out (+1 + (-1) = 0), ammonium nitrate is a neutral compound.