Which of the following represent the correct chemical formula of a compound :

1. NaSO₄
2. AlSO₄
3. NH₄PO₄
4. Ca₃N₂

Ca₃N₂

Reason — Calcium (Ca) forms a +2 ion (Ca⁺²) and nitride (N^-3) has a –3 charge.

$\text{Ca}^{2+} \space \text{N}^{3-} \\[1em] \overset{\phantom{22}{2}}{\text{Ca}} \space {\swarrow}\mathllap{\searrow} \space \overset{3}{\text{N}} \Rightarrow \underset{\phantom{2}{3}}{\text{Ca}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{2}{2}}{\text{N}} \\[1em] \text{Ca}$3\text{N}2

It is perfectly balanced. Therefore, Ca₃N₂ is correct.