Astudent studying this equilibrium begins with an equilibrium mixture that is light pink. what change will the student observe when the solution containing fe3+ ion is added to this mixture

In this case the reaction shift will favor a forward reaction. The solution will become darker or more red. This has to do with  Le Chateliers principle because by adding more reactant the equilibrium favors the forward reaction to the right. Here it is all about Le Chateliers principle that can be used to predict the effect of a change in conditions on a chemical equilibrium.