During the electron transport system (ETS) in mitochondria, which...

The electron transport system in mitochondria consists of several enzyme complexes.

Complex I is NADH dehydrogenase.

Complex II is succinate dehydrogenase.

Complex III is cytochrome $bc_1$ complex.

Complex IV is cytochrome $c$ oxidase, which contains cytochromes $a$ and $a_3$, along with two copper centres.

Complex V is ATP synthase.

Answer: Cytochrome $c$ oxidase