Question:

Consider the following species:
(i) $\text{ClO}^-$
(ii) $\text{ClO}_2^-$
(iii) $\text{ClO}_3^-$
(iv) $\text{ClO}_4^-$
Among them, the species that undergoes(undergo) disproportionation reactions is(are):

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Disproportionation is thermodynamically favorable for intermediate oxidation states. If a species contains an element in its absolute maximum oxidation state, it is exclusively an oxidizing agent and cannot disproportionate.
Updated On: Jun 16, 2026
  • (i), (ii), and (iii) only
  • (iv) only
  • (i) and (ii) only
  • (iii) and (iv) only
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The Correct Option is A

Solution and Explanation

Step 1: Understanding the Question:
The question asks us to identify which of the given chlorine oxyanion species are capable of undergoing disproportionation (a redox reaction where a single species is simultaneously oxidized and reduced).

Step 2: Key Formula or Approach:
For an element in a specific species to undergo disproportionation, it must exist in an intermediate oxidation state.
1. If the element is in its maximum possible oxidation state, it can only be reduced, so it cannot undergo disproportionation.
2. If the element is in its minimum possible oxidation state, it can only be oxidized, so it cannot undergo disproportionation.

Step 3: Detailed Explanation:

• Let us calculate the oxidation state of chlorine (Cl) in each of the given species:
itemize

• (i) In $\text{ClO}^-$: Let the oxidation state of Cl be $x$.
\[ x + (-2) = -1 \implies x = +1 \]

• (ii) In $\text{ClO}_2^-$: Let the oxidation state of Cl be $y$.
\[ y + 2(-2) = -1 \implies y = +3 \]

• (iii) In $\text{ClO}_3^-$: Let the oxidation state of Cl be $z$.
\[ z + 3(-2) = -1 \implies z = +5 \]

• (iv) In $\text{ClO}_4^-$: Let the oxidation state of Cl be $w$.
\[ w + 4(-2) = -1 \implies w = +7 \]

Chlorine is a Group 17 halogen, so its possible oxidation states range from $-1$ to $+7$.
In the perchlorate ion, $\text{ClO}_4^-$, the oxidation state of chlorine is $+7$, which is its maximum possible oxidation state. Since it cannot be oxidized any further, it cannot undergo disproportionation.
In $\text{ClO}^-$, $\text{ClO}_2^-$, and $\text{ClO}_3^-$, the oxidation states ($+1$, $+3$, and $+5$) are intermediate.
Therefore, these species can be both oxidized to higher states (like $+5$ or $+7$) and reduced to lower states (like $-1$), meaning they readily undergo disproportionation reactions.
itemize

Step 4: Final Answer:
Therefore, only species (i), (ii), and (iii) can undergo disproportionation (Option A).
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