Which of the following reactions is an example of redox reaction?

A
${Cr}_{2} O_{3} + 6 HCl \to 2 {CrCl}_{3} + 3 H_{2} O$
B
$2 {CrO}_{4}^{2 -} + H^{+} ⇌ {Cr}_{2} O_{7}^{2 -} + {OH}^{-}$
C
${Cr}_{2} O_{4}^{2 -} + 6 I^{-} + 14 H^{+} \to 2 {Cr}^{3 +} + 3 I_{2} + 7 H_{2} O$
D
${CrO}_{3} + 2 NaOH \to {Na}_{2} {CrO}_{4} + H_{2} O$

Solution:

In reactions (a), (b) and (d), no change in oxidation numbers of elements occur. Only in the choice (c), the oxidation number of Cr changes from +6 to +3 while that of l from -1 to 0.

An exchange of chemical energy between an oxidizing agent and a reducing agent During the reaction, the oxidizing ingredient loses electrons while the reducing substance receives them.

Solution:

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