Question

Which of the following is not a redox reaction?

• A. $CaCO_{3}\overset{}{ \rightarrow }CaO+CO_{2}$
• B. $O_{2}+2H_{2}\overset{}{ \rightarrow }2H_{2}O$
• C. $Na+H_{2}O\overset{}{ \rightarrow }NaOH+1/2H_{2}$
• D. $3H_{3}\left(AsO\right)_{3 \left(\right. aq \left.\right)}+BrO_{3 \left(\right. aq \left.\right)}^{-}\overset{}{ \rightarrow }Br_{\left(\right. aq \left.\right)}^{-}+3H_{3}\left(AsO\right)_{4 \left(\right. aq \left.\right)}$

Answer 1

Answer: (A)

$CaCO_{3}\overset{}{ \rightarrow }CaO+CO_{2}$
When the oxidation number of the element increases, it is oxidation and when it decreases, it is reduction.
But in the above reaction, the oxidation number of $Ca$ remains as $+2$ , $C$ remains as $+4$ and $O$ remains as $-2$ . Hence, it is not a redox reaction.