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JEE Main levelSingle correct optionDifficulty 2 of 3df094

Which statement correctly describes what happens when alkali is added to an orange acidified solution of $K X_{2} Cr X_{2} O X_{7}$ ?

AThe colour changes to yellow and the oxidation state of Cr remains $+ 6$
BThe colour changes to green because Cr is reduced to $+ 3$
CThe colour changes to yellow because Cr is reduced to $+ 3$
DThe colour changes to blue because $CrO X_{5}$ is formed

Answer: A

2 CrO X_{4} X^{2 -} + 2 H X^{+} ⇌ Cr X_{2} O X_{7} X^{2 -} + H X_{2} O

is a pH-dependent equilibrium. Added

OH X^{-}

consumes

H X^{+}

and shifts it to yellow chromate. Both ions have Cr(VI), so no redox change occurs.

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