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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3df163

Which of the following statements about the aqueous chromate-dichromate system are correct?

AThe colours of both ions arise from ligand-to-metal charge transfer.
BConversion of $Cr X_{2} O X_{7} X^{2 -}$ to $CrO X_{4} X^{2 -}$ by base is not a redox reaction.
CBoth $CrO X_{4} X^{2 -}$ and $Cr X_{2} O X_{7} X^{2 -}$ are diamagnetic.
DChromium has a $3 d^{2}$ configuration in both ions.

Answer: A, B, C

In both ions chromium is +6, so the change is an acid-base/condensation process with no change in oxidation state. Cr(VI) is

3 d^{0}

, giving diamagnetism and charge-transfer colours. The

3 d^{2}

statement is wrong, since

3 d^{2}

would be Cr(IV).

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