Here's how to determine the oxidation state of nitrogen (N) in the ammonium ion (NH₄⁺):

* Hydrogen (H) typically has an oxidation state of +1.

* The overall charge of the ammonium ion (NH₄⁺) is +1.

Let 'x' represent the oxidation state of nitrogen. We can set up an equation:

x + (4 * +1) = +1

Simplifying the equation:

x + 4 = +1

Solving for x:

x = -3

Therefore, the oxidation state of nitrogen (N) in the ammonium ion (NH₄⁺) is -3.