Question

Assertion :Equivalent mass of $KMn{O}_4$ is equal to one-fifth of its molecular mass when it acts as an oxidising agent in acidic medium. Reason: Oxidation number of $Mn$ in $KMn{O}_4$ is $+7$.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

$KMn{O}_4:$ In acidic medium, $n$ factor of $KMn{O}_4$ is $5$ as

$KMn{O}_4\stackrel{acidicmedium}{\to }M{n}^{2+}$

$\left(violet\right)$ $\left(colorless\right)$

Since, the oxidation number changes by $+5$,

so, n-factor is $5$

Equivalent weight $=\frac{Molarmass}{n-factor}=\frac{M}{5}$

In acidic medium, following reaction takes place.

$Mn{O}_4^{-}+8H^{+}+5e^{-}\to M{n}^{2+}+4H_{2}O$

Oxidation number of $Mn$ in $KMn{O}_4=1+x+(4\times -2)$

$=1+x+(-8)$

$x=7$

$\therefore$Both assertion and reason are correct but reason is not the correct explanation for assertion.