A) \[{{H}_{2}}{{O}_{2}}\]
B) \[{{H}_{2}}O\]
C) dil \[HCl\]
D) conc \[HCl\]
Correct Answer: A
Solution :
[a] \[{{K}_{2}}C{{r}_{2}}{{O}_{7}}\] an orange coloured solution, on acidification with dil \[{{H}_{2}}S{{O}_{4}}\] is oxidised by \[{{H}_{2}}{{O}_{2}}\]to blue peroxide of chromium, \[Cr{{O}_{5}}\] which is unstable. \[\begin{align} & {{K}_{2}}C{{r}_{2}}{{O}_{7}}+{{H}_{2}}S{{O}_{4}}\to {{K}_{2}}S{{O}_{4}}+{{H}_{2}}C{{r}_{2}}{{O}_{7}} \\ & \left[ {{H}_{2}}{{O}_{2}}\to {{H}_{2}}O+[O] \right]\times 4 \\ & {{H}_{2}}C{{r}_{2}}{{O}_{7}}+4\,[O]\to 2Cr{{O}_{5}}+{{H}_{2}}O \\ & \overline{\underline{{{K}_{2}}C{{r}_{2}}{{O}_{7}}+{{H}_{2}}S{{O}_{4}}+4{{H}_{2}}{{O}_{2}}\to 2Cr{{O}_{5}}+{{K}_{2}}S{{O}_{4}}+5{{H}_{2}}O}} \\ \end{align}\]
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