Question

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

• A. $VO^{+}_{2} \to V_{2}O_{3}$
• B. $Na -> Na^{+}$
• C. $CrO^{2-}_{4} \to Cr_{2} O^{2-}_{7}$
• D. $Zn^{2+} \to Zn$

Answer 1

Answer: (C)

$\overset {.}{C}ro^{2-}_{4}$
$x+[(-2) \times 4]=-2$
$x=8-2=+6$
$\overset{.}{C}r_{2}O^{2-}_{7}$
$2x=14-2=12$
$x=\frac{12}{2}=+6$
In this reaction oxidation and reduction are not involved because there is no change in oxidation number.