Which of the following functional groups increases the solubility of organic compounds in water?

• A. Ethyl group ($-\mathrm{CH}{2}_2\mathrm{CH}{3}_3$)
• B. Hydroxyl group ($-\mathrm{OH}$)
• C. Phenyl group ($-C{6}_{6}H{5}_5$)
• D. Methyl group ($-\mathrm{CH}{3}_3$)

Answer: (B)

Verified step by step guidance

1. Identify the nature of each functional group in terms of polarity and ability to interact with water molecules. Water is a polar solvent, so groups that can form hydrogen bonds or have polar characteristics increase solubility.
2. Examine the ethyl group (-CH\_2CH\_3) and methyl group (-CH\_3). Both are alkyl groups, which are nonpolar and hydrophobic, so they do not increase water solubility significantly.
3. Look at the phenyl group (-C\_6H\_5), which is an aromatic ring. It is largely nonpolar and hydrophobic, so it also does not enhance solubility in water.
4. Consider the hydroxyl group (-OH). This group is polar and can form hydrogen bonds with water molecules, greatly increasing the solubility of organic compounds in water.
5. Conclude that the hydroxyl group is the functional group that increases water solubility due to its polarity and hydrogen bonding capability.