The colour changes observed when testing for reducing agents using acidified potassium heptaoxodichromate (IV) solution is

Acidified potassium heptaoxodichromate (IV) solution is a commonly used oxidizing agent. When it is added to a reducing agent, the reducing agent is oxidized, and the color of the solution changes. In the case of acidified potassium heptaoxodichromate (IV) solution, the initial color is orange. As the reducing agent reduces the potassium heptaoxodichromate (IV) to potassium heptaoxodichromate (III), the orange color disappears, and the solution turns green. The intensity of the green color can vary depending on the concentration of the reduced potassium heptaoxodichromate (III). Therefore, the correct answer is "orange to green."