Oil Layer Ensures Anaerobic Fermentation

Steps:

• Yeast ferments sugars to alcohol and CO2 only in anaerobic conditions.
• Aerobic conditions allow yeast to respire oxygen, oxidizing alcohol to CO2 and water.
• Oil floats on the mixture, forming a barrier that blocks atmospheric oxygen.
• This maintains low oxygen levels, promoting alcohol production over respiration.

Why B is correct:

• Fermentation is anaerobic by definition; oxygen triggers aerobic respiration, which inhibits alcohol yield by metabolizing ethanol.

Why the others are wrong:

• A: Alcohol dissolves in the aqueous solution naturally; oil does not affect solubility.
• C: Oil is inert and nutrient-free; yeast relies on added sugars for energy.
• D: Oil does not trap CO2, a gaseous byproduct that escapes regardless.

Final answer: B