Final answer:
The correct formula for the compound containing the ions Mg²⁺ and N³⁻ is Mg₃N₂.
Step-by-step explanation:
The correct formula for the compound containing the ions Mg²⁺ and N³⁻ is Mg₃N₂. The magnesium ion has a charge of 2+ and the nitride ion has a charge of 3-. To balance the charges, we need three magnesium ions with a total charge of 6+ and two nitride ions with a total charge of 6-. This gives us the formula Mg₃N₂.