A student made a graph to show the chemical equilibrium position of a reaction. The student forgot to label the y-axis of the graph.

What best explains the label that the student should use on the y-axis?

Reaction rate, as the rate of forward and back reaction become equal at equilibrium.

Reaction rate, as the rate of forward reaction increases and rate of backward reaction decreases with time.

Concentration, as the concentration of products decreases and that of reactants increase over time.

Concentration, as the concentrations of reactants and products remain constant after equilibrium is reached.