What is produced from the third stage of cellular respiration, the electron transport chain?

The correct answer will be- ATP

Explanation:

Electron transport is the last stage of the cellular respiration which represents a series of events about the transfer of the electrons through electron carriers in the inner membrane space of mitochondria.

This stage of the respiration is associated with the production of a large number of ATP molecules as the NADH and FADH₂ gets reduced to provide energy to synthesize the ATP.  

The reaction of the synthesis of ATP is catalyzed by the ATP synthase which changes conformation in response to the movement of protons across the membrane.

Thus, ATP is the correct answer.