Question: 69. Which reaction is NOT a redox reaction?
(1) \mathrm{Zn}+\mathrm{CuSO}_{4} \rightarrow \mathrm{ZnSO}_{4}+\mathrm{Cu}
(2) 2 \mathrm{KClO}_{3}+\mathrm{I}_{2} \rightarrow 2 \mathrm{KIO}_{3}+\mathrm{Cl}_{2}
(3) \mathrm{H}_{2}+\mathrm{Cl}_{2} \rightarrow 2 \mathrm{HCl}
(4) \mathrm{BaCl}_{2}+\mathrm{Na}_{2} \mathrm{SO}_{4} \rightarrow \mathrm{BaSO}_{4}+2 \mathrm{NaCl}
Answer: Option (4)
Explanation:
A redox reaction involves simultaneous oxidation and reduction,
which means there must be a change in oxidation numbers of elements.
In option (1), zinc is oxidized from 0 to +2
and copper is reduced from +2 to 0,
so it is a redox reaction.
In option (2), chlorine is reduced from +5 in \mathrm{KClO}_{3} to
0 in \mathrm{Cl}_{2},
while iodine is oxidized from 0 to +5 in \mathrm{KIO}_{3},
so it is a redox reaction.
In option (3), hydrogen is oxidized from 0 to +1
and chlorine is reduced from 0 to -1,
so it is a redox reaction.
In option (4), there is no change in oxidation numbers of any element.
It is a double displacement reaction involving ion exchange without electron transfer.
Therefore, option (4) is not a redox reaction.