Step 1: What is glycolysis?
Glycolysis is the metabolic pathway in the cytoplasm that breaks down one molecule of glucose (6 carbons) into two molecules of a 3-carbon compound.
Step 2: The end product depends on oxygen availability.
In the presence of oxygen (aerobic conditions), glycolysis ends with pyruvic acid (pyruvate). Pyruvate then enters the mitochondria to begin the Krebs cycle.
Step 3: What happens without oxygen?
In the absence of oxygen (anaerobic conditions), pyruvate is converted to lactic acid (in animals) or ethanol + CO₂ (in yeast). This is the point of difference that the question tests.
Step 4: Why are the other options wrong?
Lactic acid is the anaerobic end product, not aerobic. Acetic acid is not a direct product of glycolysis. Fatty acids are synthesised from acetyl-CoA, not directly from glycolysis.
Step 5: Conclude.
When oxygen is present, the final product of glycolysis is pyruvic acid, which is then fed into the Krebs cycle for complete oxidation.
Answer: Option (3) — Pyruvic Acid