Which of the following represents a redox reaction?

Which of the following represents a redox reaction?
  1. $\mathrm{NaOH}+\mathrm{HCl} \longrightarrow \mathrm{NaCl}+\mathrm{H}_{2} \mathrm{O}$
  2. $\mathrm{BaCl}_{2}+\mathrm{H}_{2} \mathrm{SO}_{4} \longrightarrow \mathrm{BaSO}_{4}+2 \mathrm{HCl}$
  3. $\mathrm{CuSO}_{4}+2 \mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{Cu}(\mathrm{OH})_{2}+\mathrm{H}_{2} \mathrm{SO}_{4}$
  4. $\mathrm{Zn}+2 \mathrm{HCl} \longrightarrow \mathrm{ZnCl}_{2}+\mathrm{H}_{2}$

Solution

(a) and (b) are neutralisation reactions. The oxidation state of $\mathrm{Cu}$ is $+2$ in both reactant
and product, and $\mathrm{SO}_{4}^{2-}$ ion does not change. In option (d) is a redox reaction.
$\mathrm{Zn} ightarrow \mathrm{Zn}^{2+}+2 \mathrm{e}^{-}$ (Oxidation)
$2 \mathrm{H}^{+}+2 \mathrm{e}^{-} ightarrow \mathrm{H}_{2}$ (Reduction)

Asked in: JEE-TOPICTESTS-CHEMISTRY

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