The correct expression of the reaction quotient for $\mathrm{N}{}_2(\mathrm{g})+3\mathrm{H}{}_2(\mathrm{g})\rightleftharpoons 2\mathrm{NH}{}_3(\mathrm{g})$ in terms of concentrations is

1. A$Q_c=\frac{[\mathrm{NH}{}_3]}{[\mathrm{N}{}_2][\mathrm{H}{}_2]}$
2. B$Q_c=\frac{[\mathrm{NH}{}_3{]}^2}{[\mathrm{N}{}_2][\mathrm{H}{}_2{]}^3}$
3. C$Q_c=\frac{[\mathrm{NH}{}_3{]}^2}{[\mathrm{N}{}_2][\mathrm{H}{}_2]}$
4. D$Q_c=\frac{[\mathrm{N}{}_2][\mathrm{H}{}_2{]}^3}{[\mathrm{NH}{}_3{]}^2}$