Write the chemical formula of Magnesium nitride in a step-by-step manner.

Step 1 — Write each symbol with its valency

$\text{Mg}^{2+} \phantom{\nearrow} \text{N}^{3-}$

Step 2 — Interchange the valencies

$\overset{\phantom{2}{2}}{\text{Mg}} \space {\searrow}\mathllap{\swarrow} \space \overset{3}{\text{N}} \Rightarrow \underset{\phantom{1}{3}}{\text{Mg}} \space {\searrow}\mathllap{\swarrow} \space \underset{2}{\text{N}} \\[0.5em]$

Step 3 — Write the interchanged number & hence the formula

Therefore, we get

Formula of Magnesium nitride : $\bold{Mg$3N2}