For ${\mathrm{H}}_2+{\mathrm{Cl}}_2\stackrel{\text{ hษ }}{\to }2\mathrm{HCl}$, rate of reaction at $\mathrm{t}=0$ is given by rate $=-\frac{\mathrm{d}}{\mathrm{dt}}\left[{\mathrm{H}}_2\right]=6\times {10}^{-3}\mathrm{M}-{\min }^{-1}$, then rate of the reaction at $\mathrm{t}=30 \min$ is

The given reaction is:

 ${\mathrm{H}}_2+{\mathrm{Cl}}_2\stackrel{\text{ hv }}{\to }2\mathrm{HCl}$

It is a photochemical reaction, due to which it is a zero-order reaction.

The rate law for the reaction can be written as:

 $=-\frac{\mathrm{d}}{\mathrm{dt}}\left[{\mathrm{H}}_2\right]=-\frac{\mathrm{d}}{\mathrm{dt}}\left[{\mathrm{Cl}}_2\right]= \frac{1}{2}\frac{\mathrm{d}}{\mathrm{dt}}\left[\mathrm{HCl}\right]$

The given value is $=-\frac{\mathrm{d}}{\mathrm{dt}}\left[{\mathrm{H}}_2\right]=6\times {10}^{-3}\mathrm{M}-{\min }^{-1}$

So, for Chlorine it will be:

 $=-\frac{\mathrm{d}}{\mathrm{dt}}\left[{\mathrm{Cl}}_2\right]=6\times {10}^{-3}\mathrm{M}-{\min }^{-1}$

For Ammonia it will be:

 $=\frac{1}{2}\frac{\mathrm{d}}{\mathrm{dt}}\left[\mathrm{HCl}\right]=\frac{6\times {10}^{-3}\mathrm{M}-{\min }^{-1}}{2}=3\times {10}^{-3}\mathrm{M}-{\min }^{-1}$