Assign oxidation numbers to, 3Mg(s) + N2(g) = Mg3N2(s)?

3Mg(s) + N₂(g) → Mg₃N₂(s)

On the reactant side :
Oxidation number of Mg in Mg = 0
Oxidation number of N in N₂ = 0

On the produce side :
Oxidation number of Mg in Mg₃N₂ = +2 (because it is Mg²⁺ ion)
Oxidation number of N in Mg₃N₂ = -3 (because it is N³⁻ ion)

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