Which of the following statements about free radicals is true?

• A. Free radicals are always negatively charged species.
• B. Free radicals contain at least one unpaired electron.
• C. Free radicals are stable and rarely react with other molecules.
• D. Free radicals only exist in ionic compounds.

Answer: (B)

Verified step by step guidance

1. Understand what a free radical is: A free radical is a species that contains at least one unpaired electron in its outer shell. This unpaired electron makes the radical highly reactive.
2. Analyze the charge of free radicals: Free radicals are not necessarily negatively charged; they can be neutral or have various charges, but the defining feature is the unpaired electron, not the charge.
3. Consider the stability of free radicals: Because of the unpaired electron, free radicals are generally very reactive and unstable, meaning they readily react with other molecules to pair their unpaired electron.
4. Evaluate the existence of free radicals in compounds: Free radicals are not limited to ionic compounds; they can exist in many types of chemical environments, including covalent molecules and gases.
5. Conclude that the true statement is that free radicals contain at least one unpaired electron, which is the key characteristic distinguishing them from other species.