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Chemistry Question on Classical Idea Of Redox Reactions – Oxidation And Reduction Reactions

Which of the following reactions is a redox reaction

A

CaCO3+2HCl⟶CaCl2+H2O+CO2CaCO _{3}+2 HCl \longrightarrow CaCl _{2}+ H _{2} O + CO _{2}

B

AgNO3+KI⟶Agl+KNO3AgNO _{3}+ KI \longrightarrow Agl + KNO _{3}

C

Cl2+2Br−⟶Br2+2Cl−Cl _{2}+2 Br ^{-} \longrightarrow Br _{2}+2 Cl ^{-}

D

BaCl2+SO42−⟶BaSO4+2Cl−BaCl _{2}+ SO _{4}^{2-} \longrightarrow BaSO _{4}+2 Cl ^{-}

Answer

Cl2+2Br−⟶Br2+2Cl−Cl _{2}+2 Br ^{-} \longrightarrow Br _{2}+2 Cl ^{-}

Explanation

Solution

Cl2+2Br−⟶Br2+Cl−Cl _{2}+2 Br ^{-} \longrightarrow Br _{2}+ Cl ^{-} is a redox reaction as it involves both oxidation and reduction reactions simultaneously.

In the other options (a), (b) and (d) there is no change in oxidation state of any atom, hence these are not redox reaction.

(A) Ag+1N+5O3−2+K+1I−1⟶Ag+1I−1+K+1N+5O3−2\overset{+1}{Ag}\overset{+5}{N}\overset{-2}{O_3} + \overset{+1}{K} \overset{-1}{I} \longrightarrow \overset{+1}{Ag} \overset{-1}{I} + \overset{+1}{K} \overset{+5}{N} \overset{-2}{O_3}

(B) Ba+2Cl2−2+SO2−4⟶Ba+2SO4−2+2 Cl−\overset{+2}{Ba}\overset{-2}{Cl_2} + SO^{2-}{4} \longrightarrow \overset{+2}{Ba} S \overset{-2}{O_4} + 2\,Cl^-

(C) Ca+2C+4O3−2+2H+1 CI−1⟶Ca+2CI2−1+Ca−1Cl2−1+H2−1O−2+C+4O2−2\overset{+2}{Ca}\overset{+4}{C}\overset{-2}{O_3} + 2 \overset{+1}{H} \,C\overset{-1}{I} \longrightarrow \overset{+2}{Ca} C \overset{-1}{I_2} + \overset{-1}{Ca} C \overset{-1}{l_2} + \overset{-1}{H_2}\overset{-2}{O} + \overset{+4}{C} \overset{-2}{O_2}