A yellow aqueous solution of potassium chromate is acidified to form an orange species X . This species X is then reacted with a reducing agent in an acidic medium to form a green species Y . The sum of the oxidation states of chromium in the yellow starting material, the orange species X , and the green species Y is

Step-by-step solution

The yellow starting material is potassium chromate, which contains the chromate ion ( CrO ₄²⁻ ). Let the oxidation state of chromium in chromate be x . x + 4(-2) = -2 x = +6 Upon acidification, the yellow chromate ion is converted to the orange dichromate ion ( Cr ₂ O ₇²⁻ ), which is species X . This is a non-redox interconversion. Let the oxidation state of chromium in dichromate be y . 2y + 7(-2) = -2 2y = +12 y = +6 In an acidic medium, the dichromate ion (species X ) acts as an oxidizing agent and gets reduced