Spectator at or comes from the latin specs meaning

ATP synthesis is done as the electrons move through the  1 2 3 and 4 and hydrogen ion is pushed to the intermembrane space. As the hydrogen ion comes back to the matrix through the ATP synthase enzyme the ATP is produced.

Option C

ATP synthesis takes place in the mitochondria. All the hydrogen carriers get saturated through the glycolisis and the Kreb's Cycle. As these carriers comes to the inner membrane of mitochondria, there are four complexes of different electron carriers. goes to the complex 1 and goes to the complex 2.

Each complex takes the hydrogen ion from the carriers and pushes them to the intra Membranous space of the mitochondria. There the hydrogen ion concentration increases to a severe extent. As this goes on, the hydrogen ions come back to the mitochondrial matrix through a pump which is called ATP synthase which produces one ATP molecule for 3 hydrogen ion transport. Thus ATP is produced.

The oxygen is taken by cytochrome of complex 4 which is then reduced by the electrons of the hydrogen carriers and reacted with the protons to convert it to water.