Q.
In acidic medium, $H_2O_2 $ changes $ Cr_2O_7^{2-} $ to $CrO_5 $ which has two (-O-O-) bonds.
Oxidation state of Cr in $CrO_5 $ is
AIPMTAIPMT 2014Redox Reactions
Solution:
When $H_2O_2 $ is added to an acidified solution of a dichromate $Cr_2O_7^{2-} , $ a deep blue coloured complex, chromic peroxide $CrO_5 [or \, CrO(O_2)_2] $ is formed.
$Cr_2O^{2-}_7+2H^++4H_2O \rightarrow \underbrace { 2CrO(O_2)_2 }_{Chromic \, peroxide }$
$ +5H_2O $
This deep blue coloured complex has the following structure
Oxidation state of Cr is +6 due to the presence of two peroxide linkages which can be calculated as
Cr peroxide normal $ x + (-1)4+ (-2) = 0 ,x - 6 = 0 $ and $x = +6$
