Here's why:

* Electron transport chain: NADH delivers electrons to the electron transport chain in the mitochondria. These electrons move down the chain, releasing energy that is used to pump protons across the inner mitochondrial membrane.

* Proton gradient: This creates a proton gradient, which drives ATP synthesis through ATP synthase.

* ATP yield: Theoretically, the energy from NADH could generate 3 ATP molecules. However, the actual yield is slightly less due to energy losses in the process.

Therefore, each NADH molecule produces 2.5 ATP molecules.