NEET UG 2019 — Chemistry Physical Chemistry

2019mcqeasy

Which of the following reactions are disproportionation reaction?

$(a)$ $2C{u}^{+}\rightarrow C{u}^{2+}+C{u}^{0}$

$(b)$ $3Mn{O}_{4}^{2-}+4{H}^{+}\rightarrow 2Mn{O}_{4}^{-}+Mn{O}_{2}+2{H}_{2}O$

$(c)$ $2KMn{O}_{4}\overset{\Delta }{\rightarrow }{K}_{2}Mn{O}_{4}+Mn{O}_{2}+{O}_{2}$

$(d)$ $2Mn{O}_{4}^{-}+3M{n}^{2+}+2{H}_{2}O\rightarrow 5Mn{O}_{2}+4{H}^{\oplus }$

Select the correct option from the following:

Official previous-year question

Held on 30 Apr 2019 · Verified 9 Jul 2026.

Options

A
$(a)$ and $(b)$ only
B
$(a),(b)$ and $(c)$
C
$(a), (c)$ and $(d)$
D
$(a)$ and $(d)$ only

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Solution

The redox reactions in which the same species is getting oxidised (increase in oxidation number) and reduced (decrease in oxidation number).

(i) $\overset{(+1)}{2C{u}^{+}}\rightarrow \overset{(+2)}{C{u}^{+2}}+\overset{(0)}{C{u}^{0}}\rightarrow$ Disproportionation

(ii) $\overset{(+6)}{3Mn{O}_{4}^{2-}}+4{H}^{+}\rightarrow \overset{(+7)}{2Mn{O}_{4}^{-}}+\overset{(+4)}{Mn{O}_{2}}+2{H}_{2}O\rightarrow$ Disproportionation

(iii) $\overset{(+7)}{2KMn{O}_{4}}\overset{\Delta }{\rightarrow }\overset{(+6)}{{K}_{2}Mn{O}_{4}}+\overset{(+4)}{Mn{O}_{2}}+{O}_{2}$

Only reduction is happening here.

(iv) $\overset{(+7)}{2Mn{O}_{4}^{-}}+\overset{(+2)}{3M{n}^{+2}}\rightarrow \overset{(+4)}{5Mn{O}_{2}}$

Different species are getting oxidised and reduced. Hence, the correct options are (i) and (ii) only.

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Solution

The redox reactions in which the same species is getting oxidised (increase in oxidation number) and reduced (decrease in oxidation number).

(i) $\overset{(+1)}{2C{u}^{+}}\rightarrow \overset{(+2)}{C{u}^{+2}}+\overset{(0)}{C{u}^{0}}\rightarrow$ Disproportionation

(ii) $\overset{(+6)}{3Mn{O}_{4}^{2-}}+4{H}^{+}\rightarrow \overset{(+7)}{2Mn{O}_{4}^{-}}+\overset{(+4)}{Mn{O}_{2}}+2{H}_{2}O\rightarrow$ Disproportionation

(iii) $\overset{(+7)}{2KMn{O}_{4}}\overset{\Delta }{\rightarrow }\overset{(+6)}{{K}_{2}Mn{O}_{4}}+\overset{(+4)}{Mn{O}_{2}}+{O}_{2}$

Only reduction is happening here.

(iv) $\overset{(+7)}{2Mn{O}_{4}^{-}}+\overset{(+2)}{3M{n}^{+2}}\rightarrow \overset{(+4)}{5Mn{O}_{2}}$

Different species are getting oxidised and reduced. Hence, the correct options are (i) and (ii) only.

NEET UG 2019 — Chemistry Physical Chemistry

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NEET UG 2019 — Chemistry Physical Chemistry

Options

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Solution

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