Here's why:

* Mitochondrial Structure: Mitochondria have two membranes: the outer membrane and the inner membrane. The inner membrane is folded into cristae, which increases its surface area.

* ATP Production: The inner membrane is where the electron transport chain and ATP synthesis occur. ATP synthase, the enzyme responsible for ATP production, is embedded within this membrane.

* Proton Gradient: The electron transport chain creates a proton gradient across the inner mitochondrial membrane. ATP synthase utilizes this proton gradient to drive the production of ATP from ADP and inorganic phosphate.

Therefore, ATPase is specifically located within the inner mitochondrial membrane, where it plays a crucial role in ATP production.