Animated Solution for Chemistry - Redox Reactions: In which one of the following sets all species show disproportionation reaction

Mastering Disproportionation Reactions

Imagine a chemical species acting as both a hero and a villain to itself. In the fascinating world of redox chemistry, this phenomenon is known as a disproportionation reaction. It occurs when a single element in a compound is simultaneously oxidized (loses electrons) and reduced (gains electrons), splitting its identity into two different oxidation states.

There is a fundamental catch to this chemical dual-identity: The Intermediate State Rule. For an element to undergo disproportionation, it must exist in an intermediate oxidation state.

Think of it like standing on a staircase. If you are on the middle steps, you can choose to go up (oxidation) or go down (reduction). However, if you are already on the top floor (maximum oxidation state), you can only go down. Conversely, if you are in the basement (minimum oxidation state), you can only go up.

Let's apply this logic to our suspects in the given options.

Let's check option (a). We immediately spot fluorine gas, ${\text{F}}_2$. Fluorine is the undisputed king of electronegativity on the periodic table. It only exhibits oxidation states of $0$ and $-1$. Because it is already at its maximum possible state of $0$ in ${\text{F}}_2$, it can never be oxidized to a positive state. Therefore, ${\text{F}}_2$ cannot disproportionate, eliminating option (a).

Moving to option (b), we encounter the permanganate ion, ${\text{MnO}}_4^{-}$. Here, manganese is sitting at its absolute peak, a $+7$ oxidation state. It cannot climb any higher, meaning it cannot be oxidized further. Thus, option (b) is out.

In option (d), we find the perchlorate ion, ${\text{ClO}}_4^{-}$. In this ion, chlorine is maxed out at a $+7$ oxidation state. Just like permanganate, it has nowhere to go but down. Option (d) is also incorrect.

Finally, let's analyze option (c).

First, we have the chlorite ion, ${\text{ClO}}_2^{-}$. Chlorine here is in a $+3$ oxidation state, which is comfortably intermediate between its minimum of $-1$ and maximum of $+7$. It can easily disproportionate into ${\text{Cl}}^{-}$ ($-1$) and ${\text{ClO}}_3^{-}$ ($+5$).

Next is chlorine gas, ${\text{Cl}}_2$. Sitting at an oxidation state of $0$, it is also in an intermediate state and can disproportionate into ${\text{Cl}}^{-}$ ($-1$) and ${\text{ClO}}^{-}$ ($+1$) in an alkaline medium.

Lastly, the manganese ion, ${\text{Mn}}^{3+}$, is at a $+3$ state. This is intermediate for manganese, allowing it to disproportionate into ${\text{Mn}}^{2+}$ ($+2$) and ${\text{MnO}}_2$ ($+4$).

Since all the species in option (c) are in intermediate oxidation states, they possess the chemical flexibility to undergo disproportionation. Therefore, option (c) is our correct answer!