Here's how to determine the elements being oxidized and reduced in the reaction N₂ + 3H₂ → 2NH₃:

1. Assign Oxidation Numbers:

* N₂: Nitrogen in its elemental form has an oxidation number of 0.

* H₂: Hydrogen in its elemental form has an oxidation number of 0.

* NH₃:

* Hydrogen has an oxidation number of +1 (it's more electronegative than nitrogen).

* Nitrogen has an oxidation number of -3 (to balance the +3 from three hydrogen atoms).

2. Identify Changes in Oxidation Numbers:

* Nitrogen (N): The oxidation number of nitrogen goes from 0 in N₂ to -3 in NH₃. This is a reduction (gain of electrons).

* Hydrogen (H): The oxidation number of hydrogen goes from 0 in H₂ to +1 in NH₃. This is an oxidation (loss of electrons).

Conclusion:

* Nitrogen (N) is reduced.

* Hydrogen (H) is oxidized.