Which of the following organic compounds is very soluble in water?

Correct answer: CH₃COOH (acetic acid).

Explanation: Acetic acid is highly polar and both donates and accepts hydrogen bonds, making it very soluble (essentially miscible) with water.

• C₂H₂ (ethyne) and C₂H₄ (ethene) are non-polar hydrocarbons ⇒ very low solubility in water.
• CH₃COOCH₂CH₃ (ethyl acetate) is only moderately soluble; the ester can accept H-bonds but cannot donate, so it is not “very” soluble compared with acetic acid.