Solution: the correct option is A
As the reaction progresses, the reactant concentration decreases and the product concentration rises.
As a result, the rate of reaction between the reactant and the product can be calculated as follows:
![Rate=-\frac{d}{dt}[{{N}_{2}}]=-\frac{1}{3}\frac{d}{dt}[{{H}_{2}}]=+\frac{1}{2}\frac{d}{dt}[N{{H}_{3}}]](https://www.learnatnoon.com/s/wp-content/ql-cache/quicklatex.com-d7aaa1d40734714143557b92d45dea6b_l3.png "Rendered by QuickLaTeX.com")
For the elementary reaction 
