The Attempt at a Solution
What is confusing me is the wording. It merely says for the concentration of chromate. All this time we've been doing the equilibrium concentrations. Doing mole-mole with the Cr2O7 yields the answer to be D. I then assumed that it meant that they were the concentrations at equilibrium, which gave C to be the correct answer after preforming the equilibrium constant equation. Thanks for reading.