Free radical with highest activity:
**Core Concept**
The question tests knowledge of **free radicals**, highly reactive molecules containing unpaired electrons, and their role in oxidative stress and cellular damage. Understanding the reactivity of different free radicals is crucial in **pharmacology** and **pathophysiology**.
**Why the Correct Answer is Right**
The hydroxyl radical (**·OH**) is considered the most reactive free radical, capable of abstracting hydrogen atoms from molecules, leading to cellular damage. Its high reactivity stems from its strong electronegativity and ability to participate in various chemical reactions, including those damaging cellular components like **DNA**, **proteins**, and **lipids**.
**Why Each Wrong Option is Incorrect**
**Option A:** Superoxide (**·O2-**) is less reactive than the hydroxyl radical.
**Option B:** Hydrogen peroxide (**H2O2**), though a reactive oxygen species, is not a free radical itself but can generate hydroxyl radicals.
**Option D:** Peroxyl radicals (**·OOH**) are also reactive but less so than hydroxyl radicals.
**Clinical Pearl / High-Yield Fact**
Remember, the **hydroxyl radical** is the most potent oxidant among free radicals, and its formation is often a critical step in oxidative damage to biomolecules.
**Correct Answer:** D. Hydroxyl radical (·OH)