The right answer is C. Within the mitochondria’s inner membrane.
The mitochondrion is limited by two membranes of very different properties:
* the outer membrane contains a transmembrane protein, porin, which allows the passage of ions and water-soluble metabolites of molar mass <10.000 Da.
* The inner membrane is very rich in proteins and almost impermeable to ions and water-soluble metabolites.
The respiratory chain or electron transport chain is located in the inner membrane of mitochondria. Each mitochondrion contains thousands of copies of the electron transport chain.