For the reaction ${\text{N}}_{\text{2}}{\text{+ 3H}}_{\text{2}}\to {\text{ 2NH}}_{\text{3}}\text{,}$ the rate of change of concentration for hydrogen is $\text{–0}{\text{.3 × 10}}^{\text{–4}}{\text{Ms}}^{\text{–1}}\text{.}$ The rate of change of concentration of ammonia is

N₂ + 3H₂ → 2NH₃

r = - d(N₂)/dt = - (1/3) d(H₂)/dt = + (1/2) d(NH₃)/dt

Given, - d(H₂)/dt = 0.3 × 10⁻⁴ M s⁻¹

So, r ⇒ - (1/3) × 0.3 × 10⁻⁴ = + (1/2) d(NH₃)/dt

∴ d[NH₃]/dt = (2/3) × 0.3 × 10⁻⁴ = 0.2 × 10⁻⁴