A) \[NaCl+KN{{O}_{3}}\xrightarrow{{}}NaN{{O}_{3}}+KCl\]
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 :
Those reactions in which oxidation and reduction processes occur simultaneously are called redox reaction. If there is an increase in the oxidation number of given species, then it is termed as oxidation while if there is decrease in oxidation number, then it is termed as reduction. \[\overset{+1\,\,\,\,-1}{\mathop{NaCl}}\,+\overset{+1\,\,\,\,-1}{\mathop{KN{{O}_{3}}}}\,\xrightarrow{\,}\,\overset{+1\,\,\,\,\,\,-1}{\mathop{NaN{{O}_{3}}}}\,\,+\overset{+1\,\,\,-1}{\mathop{KCl}}\,\] In this case, there is no change in the oxidation number, of species involved. So, it is not a redox reaction. \[\overset{+2}{\mathop{C}}\,a\overset{-2}{\mathop{{{C}_{2}}{{O}_{4}}}}\,+\overset{+1}{\mathop{2H}}\,C\overset{-1}{\mathop{l}}\,\xrightarrow{{}}\overset{+2}{\mathop{C}}\,aC{{\overset{+1}{\mathop{l}}\,}_{2}}+\overset{+1}{\mathop{{{H}_{2}}}}\,{{C}_{2}}{{\overset{-2}{\mathop{O}}\,}_{4}}\] In this case, there is no change in the oxidation number of atom/ion/molecule. So, it is not a redox reaction. \[\overset{+2}{\mathop{C}}\,a{{(O\overset{-1}{\mathop{H}}\,)}_{2}}+\overset{+3}{\mathop{2}}\,N{{\overset{-1}{\mathop{H}}\,}_{4}}C\overset{-1}{\mathop{l}}\,\xrightarrow{{}}C\overset{+2}{\mathop{a}}\,C{{\overset{-1}{\mathop{l}}\,}_{2}}+2\overset{-3}{\mathop{N}}\,{{\overset{+1}{\mathop{H}}\,}_{3}}\] \[+2{{\overset{+1}{\mathop{H}}\,}_{2}}\overset{-2}{\mathop{O}}\,\] Here, again there is no change in the oxidation number of atoms/ions/molecules. So, it is not a redox reaction. \[2\overset{+1}{\mathop{K}}\,[A\overset{+1}{\mathop{g}}\,(CN)_{2}^{-1}]+\overset{0}{\mathop{Z}}\,n\xrightarrow{{}}2\overset{0}{\mathop{Ag}}\,+{{\overset{+1}{\mathop{K}}\,}_{2}}+[\overset{+2}{\mathop{Zn}}\,(CN)_{4}^{-1}]\] In this reaction, oxidation number of silver is \[+1\] in \[K[Ag{{(CN)}_{2}}]\] Its oxidation number changes to zero by gain of electron. Therefore, reduction occur. On the other hand, oxidation number of zinc changes from 0 to \[+2\]. Therefore, oxidation takes place at zinc. \[A{{g}^{+}}{{e}^{-}}\xrightarrow{{}}Ag\] (gain of \[{{e}^{-}}\], reduction) \[Zn-2{{e}^{-}}\xrightarrow{{}}Z{{n}^{2+}}\] loss of \[{{e}^{-}}\], oxidation)
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