The compound that makes palm wine taste sour after exposure to the air for few days is

Analyze the question: Palm wine turns sour after being left in the air for a few days. We need to identify the compound responsible for the sour taste.

Explain the concept: Fresh palm wine contains sugars that yeast ferments into ethanol (alcoholic fermentation):

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

When palm wine is exposed to air, bacteria (Acetobacter) oxidize the ethanol to ethanoic acid (acetic acid), the same acid found in vinegar:

C₂H₅OH + O₂ → CH₃COOH + H₂O

Step-by-step solution:

1. Palm wine starts out sweet because of its sugar content.
2. Yeast ferments the sugar to ethanol, which makes it alcoholic.
3. With continued exposure to air, ethanol is oxidized to ethanoic acid.
4. Acids taste sour, so ethanoic acid is the cause of the sour taste.

Checking the options:

• A. Ethanol: this is the alcohol, which gives the intoxicating effect, not the sourness.
• B. Ethanoic acid: this is correct, because it is the product of oxidation and tastes sour.
• C. Methanol: not formed in palm wine fermentation, and it is toxic.
• D. Methanoic acid: this is found in ant stings, not in souring palm wine.

Answer: B. Ethanoic acid

Exam tip: Remember the chain sugar → ethanol → ethanoic acid. Palm wine goes sour the same way wine turns to vinegar. Any question about "alcohol going sour" points to ethanoic acid.