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  4. CrO42 - (yellow) changes to Cr2O72 - (orange) in pH = x and vice-versa in pH = y. Hence, x and y are

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Q. $CrO_{4}^{2 -}$ (yellow) changes to $Cr_{2}O_{7}^{2 -}$ (orange) in pH = x and vice-versa in pH = y. Hence, x and y are

NTA AbhyasNTA Abhyas 2020The d-and f-Block Elements

Solution:

$CrO_{4}^{2 -}$ (yellow) changes to $Cr_{2}O_{7}^{2 -}$ (orange) in acidic medium so pH = x = 6.

$2CrO_{4}^{2 -}+2H^{+} \rightarrow Cr_{2}O_{7}^{2 -}+H_{2}O$

The opposite reaction takes place in basic medium so pH = y = 8.

$Cr_{2}O_{7}^{2 -}+2OH^{-} \rightarrow 2CrO_{4}^{2 -}+H_{2}O$