Question

The Fenton reaction leads to free radical generation when

• A. Radiant energy is absorbed by water
• B. Hydrogen peroxide is formed by myeloperoxidase
• C. Ferrous ions are converted into ferric ions
• D. Nitric oxide is converted into peroxynitrite anion

Hint:

Fenton reaction: Fe2+ + H2O2 gives Fe3+ + hydroxyl radical.

Answer 1

The Correct Option is C

The question is about how the Fenton reaction makes free radicals inside cells. This reaction is one of the classic ways hydrogen peroxide turns into a much more damaging hydroxyl radical.

1. Radiant energy absorbed by water: This describes radiolysis of water by radiation, a separate mechanism of radical formation that does not need iron and is not the Fenton reaction.
2. Hydrogen peroxide formed by myeloperoxidase: Myeloperoxidase actually uses hydrogen peroxide to make hypochlorous acid inside white cells, it is a different oxidative pathway and does not describe the Fenton step.
3. Ferrous ions converted into ferric ions: In the Fenton reaction, $Fe^{2+}$ reacts with $H_2O_2$ and gives up an electron, becoming $Fe^{3+}$, while the peroxide splits to release a hydroxyl radical, $OH^{\bullet}$. This electron transfer step is the Fenton reaction itself.
4. Nitric oxide converted into peroxynitrite anion: This happens when nitric oxide reacts with superoxide, a separate radical generating route that has nothing to do with iron or Fenton chemistry.

So among the four choices, only the change of ferrous to ferric iron matches the actual chemistry of the Fenton reaction, $Fe^{2+}+H_2O_2 \to Fe^{3+}+OH^{-}+OH^{\bullet}$.

Let's summarize:

• Fenton reaction needs a metal ion, classically iron, reacting with hydrogen peroxide.
• The metal is oxidised, here ferrous to ferric, while a hydroxyl radical is released.
• Radiolysis and the nitric oxide, superoxide pathway are different radical-forming routes.

The correct answer is that ferrous ions are converted into ferric ions.