Question

Photo attached. Equilibrium question. I know that the answer is C, but why?

Answer 1

Count the quantity of each particle in the container in each of the diagrams:

$\begin{array}{cccc} \text{H}_2 & \text{I}_2 & \text{HI} & \\3 & 3 & 0 & \text{as in figure i} \\2 & 2 & 2 & \text{as in figure ii} \\1 & 1 & 4 & \text{as in figure iii} \\1 & 1 & 4 & \text{as in figure iv}\\1 & 1 & 4 & \text{as in figure v} \\\end{array}$

The container appears to be of constant volume and thus the concentration of each species is directly related to the number of particle present. By definition, the system is in equilibrium once the relative concentration becomes constant, which is in this scenario achieved at the time point depicted in diagram iii. Thus the answer.