Which of the following is considered a functional group in organic chemistry rather than simply a group in the periodic table?

• A. Halogen group
• B. Alkali metal group
• C. Hydroxyl group ($-OH$)
• D. Noble gas group

Answer: (C)

Verified step by step guidance

1. Understand that in organic chemistry, a functional group is a specific group of atoms within molecules that is responsible for the characteristic chemical reactions of those molecules.
2. Recognize that groups like the halogen group, alkali metal group, and noble gas group refer to elements classified in the periodic table based on their properties, not specific functional groups in organic molecules.
3. Identify the hydroxyl group, represented as \(-\mathrm{OH}\), as a functional group because it consists of an oxygen atom bonded to a hydrogen atom and is commonly found in alcohols and other organic compounds.
4. Recall that the presence of the hydroxyl group in a molecule significantly influences its chemical behavior, such as increasing polarity and enabling hydrogen bonding.
5. Conclude that among the options, the hydroxyl group is the functional group in organic chemistry, while the others are elemental groups from the periodic table.