Question

Which one of the following reactions does not involve either oxidation or reduction.

• A. $VO_{2}^{+} \rightarrow V_{2}O_{3}$
• B. $Na \rightarrow Na^{+}$
• C. $CrO_{4}^{2 -} \rightarrow Cr_{2}O_{7}^{2 -}$
• D. $Zn^{2 +} \rightarrow Zn$

Answer 1

Answer: (C)

$CrO_{4}^{2 -} \rightarrow Cr_{2}O_{7}^{2 -}$

Answer 2

$\overset{*}{CrO_{4}^{2 -}}$ $\overset{*}{Cr_{2}O_{7}^{2 -}}$

$x + \lbrack( - 2) \times 4\rbrack = - 2$ $2x + ( - 2) \times 7 = - 2$

$x = 8 - 2 = + 6$ $2x = 14 - 2 = 12$,

$x = \frac{12}{2} = + 6$

In this reaction oxidation and reduction are not involved because there is no change in oxidation number.