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

 [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.