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Question

Chemistry Question on Redox reactions

Which of the following reaction involves neither oxidation nor reduction

A

\ceCrO42−−>Cr2O72−\ce{CrO^{2-}_4 -> Cr_2O^{2-}_7}

B

\ceCr−>CrCl3\ce{Cr -> CrCl3}

C

\ceNa−>Na+\ce{Na -> Na^{+}}

D

\ce2S2O32−−>S4O62−\ce{2S_2O_3^{2-} -> S_4O_6^{2-}}

Answer

\ceCrO42−−>Cr2O72−\ce{CrO^{2-}_4 -> Cr_2O^{2-}_7}

Explanation

Solution

Oxidation number of CrCr in CrO42−CrO _{4}^{2-} =x+4×(−2)=−2= x +4 \times(-2)=-2 ⇒x=6\Rightarrow x=6 Oxidation number of CrCr in Cr2O72−Cr _{2} O _{7}^{2-} =2x+7×(−2)=−2=2 x +7 \times(-2)=-2 ⇒x=6\Rightarrow x=6 The oxidation number of Cr does not change. Hence, it undergoes neither oxidation nor reduction.