If acidified Potassium Dichromate(VI) (K$_2$Cr$_2$O$_7$) acts as oxidizing agent, color changes from

Analysis

The question asks for the characteristic color change observed when acidified potassium dichromate(VI) ($K_2Cr_2O_7$) functions as an oxidizing agent in a chemical reaction.

Concept Explanation

Potassium dichromate(VI) is a strong oxidizing agent commonly used in organic chemistry (for example, to test for primary and secondary alcohols or to oxidize aldehydes to carboxylic acids).

In its original state, the dichromate ion ($Cr_2O_7^{2-}$) is orange. When it acts as an oxidizing agent, it undergoes a reduction reaction. The chromium atom is reduced from an oxidation state of +6 to +3. The resulting chromium(III) ion ($Cr^{3+}$) in an aqueous solution is green.

The half-equation for this reduction is: $Cr_2O_7^{2-} + 14H^+ + 6e^- \rightarrow 2Cr^{3+} + 7H_2O$

Step-by-Step Solution

1. Identify the reactant: Acidified potassium dichromate(VI) contains the dichromate ion ($Cr_2O_7^{2-}$), which is naturally orange.
2. Identify the process: As an oxidizing agent, it accepts electrons from the substance being oxidized.
3. Identify the product: During this reduction process, the chromium is converted into the chromium(III) ion ($Cr^{3+}$).
4. Observe the color change: The solution transitions from the color of the dichromate ion (orange) to the color of the chromium(III) ion (green).

Conclusion

The color change is from orange to green. This matches option B.

Exam Tip: Don't confuse this with Potassium Chromate ($K_2CrO_4$), which is yellow. Remember: Dichromate is Orange (like a sunset), and Chromate is Yellow (like a lemon).