Which reaction involves neither oxidation nor reduction?

Which reaction involves neither oxidation nor reduction?
  1. $\mathrm{CrO}_{4}^{2-} \longrightarrow \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}$
  2. $\mathrm{Cr} \longrightarrow \mathrm{CrCl}_{3}$
  3. $\mathrm{Na} \longrightarrow \mathrm{Na}^{+}$
  4. $2 \mathrm{~S}_{2} \mathrm{O}_{3}^{2-} \longrightarrow \mathrm{S}_{4} \mathrm{O}_{6}^{2-}$

Solution

$\mathrm{O}$. $\mathrm{N}$. of $\mathrm{Cr}$ on both sides is $+6$.

Asked in: JEE-TOPICTESTS-CHEMISTRY

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