We have an oxidation reaction that occurs in an acid medium due to the presence of H3O+ ions. If we add NaOH, this strong base will tend to neutralize the H3O+ ions, forming water and lowering the concentration of H3O+ ions.
As the concentration of the products decreases, the reaction will tend to shift towards the formation of more products, to the right. That is, to the formation of more moles of CrO4(-2).
Therefore, you are correct. The answer will be C, since the balance is displaced because of the concentration of the products changes. And as there are more moles of CrO4(-2) the mixture will turn more yellow.
Answer: C