Which statement correctly defines disproportionation?

• A. Oxidizer
• B. Peroxide Forming
• C. Pyrophoric
• D. Disproportionation

Answer: (D)

Disproportionation is a redox process where a single chemical species is simultaneously oxidized and reduced to form two products with the element in different oxidation states. A classic example is the decomposition of hydrogen peroxide: 2 H2O2 → 2 H2O + O2. Here, the oxygen in H2O2 is in an intermediate oxidation state; one part is reduced to water (oxidation state goes down) and another part is oxidized to oxygen gas (oxidation state goes up). This illustrates how the same species splits into two forms through internal electron transfer.

The other statements describe properties or roles (an oxidizer, peroxide forming, pyrophoric) rather than the process of a species changing oxidation state to yield two different products. So the term that defines this phenomenon is disproportionation.