To determine which species does not undergo a disproportionation reaction, we need to understand the concept of disproportionation. A disproportionation reaction is a type of redox reaction in which a single species undergoes both oxidation and reduction, forming two different products.
Let's analyze each given option in the context of chlorine compounds:
- : In the disproportionation reaction, this ion can form (oxidation) and (reduction).
- : This can disproportionate to form higher oxidation state species such as and lower states such as .
- : This ion can also undergo disproportionation, forming (oxidation) and (reduction).
- : In this case, the oxidation state of chlorine in is +7, which is its highest possible oxidation state. Because it cannot be oxidized further, it cannot undergo disproportionation.
Conclusion: Thus, the species that does not undergo a disproportionation reaction is because it is already in its highest oxidation state.