Which of the following is an example of a functional group in organic chemistry?

• A. Helium atom ($\mathrm{He}$)
• B. Hydroxyl group ($-OH$)
• C. Chloride ion ($\mathrm{Cl}-$)
• D. Sodium ion ($\mathrm{Na}+$)

Answer: (B)

Verified step by step guidance

1. Understand that a functional group in organic chemistry is a specific group of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules.
2. Recognize that functional groups are often used to classify organic compounds and predict their reactivity.
3. Identify the options given: Helium atom (He), Hydroxyl group (-OH), Chloride ion (Cl-), and Sodium ion (Na+).
4. Note that the hydroxyl group (-OH) is a common functional group found in alcohols and is responsible for their chemical properties.
5. Conclude that the hydroxyl group (-OH) is the example of a functional group in organic chemistry among the given options.