question_answer

Which of the following is a redox reaction?

A) \[NaCl+KN{{O}_{3}}\xrightarrow{{}}NaN{{O}_{2}}+KCl\]

B) \[Ca{{C}_{2}}{{O}_{4}}+2HCl\xrightarrow{{}}CaC{{l}_{2}}+{{H}_{2}}{{C}_{2}}{{O}_{4}}\]

C) \[Ca\,{{(OH)}_{2}}+2N{{H}_{4}}Cl\xrightarrow{{}}CaC{{l}_{2}}+2N{{H}_{3}}+2{{H}_{2}}O\]

D) \[2K\,[Ag\,{{(CN)}_{2}}+Zn\xrightarrow{{}}2Ag+{{K}_{2}}[Zn\,{{(CN)}_{4}}]\]

Correct Answer: D

Solution :

[a]

[b]

[c]

In all these cases during reaction, there is no change in oxidation state of ion or molecule or constituent atom, thus these are simply ionic reactions.

[d]

\[\begin{align}   & 2K[Ag{{\left( CN \right)}_{2}}]+Zn\to 2Ag \\  & +{{K}^{2}}[Zn{{\left( CN \right)}_{4}}] \\ \end{align}\]

\[A{{g}^{+}}\xrightarrow{{}}Ag\]gain of \[{{e}^{-}},\]reduction

\[Zn\xrightarrow{{}}Z{{n}^{2+}}\] loss of \[{{e}^{-}},\] oxidation.

As both oxidation and reduction takes place simultaneously.

Thus, it is a redox reaction.