Which of the following species does not show disproportionation reaction?

Question

Accepted Answer

The correct option is (4):

To understand why $\mathrm{ClO_{4}^{\ominus}}$ does not show a disproportionation reaction, we first need to define what a disproportionation reaction is. A disproportionation reaction is a specific type of redox reaction where a single element in a given species is simultaneously oxidized (its oxidation state increases) and reduced (its oxidation state decreases) to form two different products. For an element to undergo disproportionation, it must exist in an intermediate oxidation state, meaning it can both increase and decrease its oxidation state.

Let's calculate the oxidation state of chlorine in each of the given species:1.  For $\mathrm{ClO^{\ominus}}$: Let the oxidation state of $\mathrm{Cl}$ be $x$.
    $x + (-2) = -1 \Rightarrow x = +1$.
    Chlorine in $\mathrm{ClO^{\ominus}}$ is in the $+1$ oxidation state. Chlorine can have oxidation states ranging from $-1$ to $+7$. Since $+1$ is an intermediate oxidation state, it can be both oxidized (to $+3, +5, +7$) and reduced (to $-1, 0$). Hence, $\mathrm{ClO^{\ominus}}$ can undergo disproportionation.

2.  For $\mathrm{ClO\_{2}^{\ominus}}$: Let the oxidation state of $\mathrm{Cl}$ be $y$.
    $y + 2(-2) = -1 \Rightarrow y - 4 = -1 \Rightarrow y = +3$.
    Chlorine in $\mathrm{ClO\_{2}^{\ominus}}$ is in the $+3$ oxidation state, which is an intermediate oxidation state. It can be oxidized to higher states ($+5, +7$) and reduced to lower states ($+1, 0, -1$). Thus, $\mathrm{ClO\_{2}^{\ominus}}$ can undergo disproportionation.

3.  For $\mathrm{ClO\_{3}^{\ominus}}$: Let the oxidation state of $\mathrm{Cl}$ be $z$.
    $z + 3(-2) = -1 \Rightarrow z - 6 = -1 \Rightarrow z = +5$.
    Chlorine in $\mathrm{ClO\_{3}^{\ominus}}$ is in the $+5$ oxidation state, another intermediate state. It can be oxidized to $+7$ and reduced to lower states ($+3, +1, 0, -1$). Therefore, $\mathrm{ClO\_{3}^{\ominus}}$ can undergo disproportionation.

4.  For $\mathrm{ClO\_{4}^{\ominus}}$: Let the oxidation state of $\mathrm{Cl}$ be $w$.
    $w + 4(-2) = -1 \Rightarrow w - 8 = -1 \Rightarrow w = +7$.
    Chlorine in $\mathrm{ClO\_{4}^{\ominus}}$ is in the $+7$ oxidation state. This is the maximum possible oxidation state for chlorine. Since chlorine cannot be oxidized further (it cannot attain an oxidation state higher than $+7$), $\mathrm{ClO\_{4}^{\ominus}}$ cannot undergo a disproportionation reaction. It can only be reduced.The incorrect option is (1): $\mathrm{ClO^{\ominus}}$ can undergo disproportionation because chlorine is in the $+1$ oxidation state, which is an intermediate state allowing for both oxidation to higher states and reduction to lower states.
The incorrect option is (2): $\mathrm{ClO\_{2}^{\ominus}}$ can undergo disproportionation because chlorine is in the $+3$ oxidation state, an intermediate state that permits both further oxidation and reduction.
The incorrect option is (3): $\mathrm{ClO\_{3}^{\ominus}}$ can undergo disproportionation because chlorine is in the $+5$ oxidation state, an intermediate state enabling both oxidation to a higher state and reduction to lower states.