Question

Which from the following hydroxy compounds contain only one \(-\text{OH}\) group in a molecule?

• A. Crotonyl alcohol
• B. Ethylene glycol
• C. Pyrogallol
• D. Hydroquinone

Hint:

Count the OH groups: crotyl alcohol has one; glycol has two; pyrogallol has three; hydroquinone has two.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Alcohols and phenols are classified as mono-, di- or trihydric by the number of \(-\text{OH}\) groups.

Step 2: Count the OH Groups:
Crotonyl (crotyl) alcohol: \(\text{CH}_3\text{CH}=\text{CHCH}_2\text{OH}\), one OH.
Ethylene glycol: \(\text{HOCH}_2\text{CH}_2\text{OH}\), two OH.
Pyrogallol: benzene-1,2,3-triol, three OH.
Hydroquinone: benzene-1,4-diol, two OH.

Step 3: Conclusion:
Only crotonyl alcohol is monohydric, so (A) is correct.

Final Answer:
Crotonyl alcohol has a single OH group, option (A). \[ \boxed{\text{(A) Crotonyl alcohol}} \]