Question

Which of the following explanation is correct about the given below reaction?

\[\ce{Cr2O^2-_7 + H2O -> 2CrO^2-_4 + 2H+}\]

Options

• Cr is reduced

• Cr is oxidised

• Oxidation number of Cr has neither decreased nor increased

• Hydrogen is reduced

Answer 1

Oxidation number of Cr has neither decreased nor increased

Explanation:

\[\begin{array}{cc}
\ce{Cr2C^{2-}_7 + H2O -> 2CrO^{2-}_4 + 2H+}\\
\underset{+6}{\downarrow}\phantom{.......}\underset{+1}{\downarrow}\phantom{.......}\underset{+6}{\downarrow}\phantom{.......}\underset{+1}{\downarrow}\phantom{...}\end{array}\]

The oxidation number of Cr in \[\ce{Cr2O^{2-}_7 and CrO^{2-}_4}\] is same, i.e. 6.
Thus, oxidation of Cr has neither decreased nor increased.