Oxidation reaction involves loss of electrons, and reduction reaction involves gain of electrons. The reaction in which a species disproportinates into two oxidation states ( lower and higher) is called disproportionation reaction.
Which of the following is not a dispropotional reaction?

Options

A. `Cu_(2)O+2H^(+) to Cu+Cu^(+)+H_(2)O`
B. `2CrO_(4)^(2-) +2H^(+) to Cr_(2)O_(7)^(2-)+H_(2)O`
C. `CaCO_(3)+2H^(+) to Ca^(2+)+H_(2)O+CO_(2)`
D. `Cr_(2)O_(7)^(2-) to 2CrO_(4)^(2-)+H_(2)O`