Witch step of cellular respiration will not take place in the absence of oxygen

The answer is; glycolysis

This process converts glucose molecule to pyruvate. It is an oxygen-independent pathway, unlike the Krebs cycle. Glycolysis occurs in the cell cytoplasm while the Krebs cycle (aerobic pathway) occurs in the mitochondria. In the presence of oxygen, the product of glycolysis, i. e pyruvate, is fed to the Krebs cycle. If oxygen is unavailable the pyruvate is converted to lactate.