Answer
a. Green is $H_2$, blue is $N_2$ and red is $NH_3$.
The balanced equation for this reaction is:
$$N_2 + 3H_2 \longrightarrow 2 NH_3$$
Looking at the first diagram, we have $H_2$ with the greatest concentration, a little bit of $N_2$ and no $NH_3$
Looking at the start of each plot, we can associate each compound to their relative initial concentration. $H_2$ will be the plot that start at the highest point, $N_2$ the second higher, and $NH_3$ will start at 0.
b. Green and blue are decreasing because $H_2$ and $N_2$ are reactants, and red is increasing because $NH_3$ is a product.
c. Equilibrium is reach a little after the middle of that graph. We know that because all the concentrations are constant after that.
Work Step by Step
Remember: Blue sphere = Nitrogen, White sphere = Hydrogen.
