Each complex in the electron transport chain collectively acts as a pump that removes H+ from the mitochondrial matrix and pumps it into the space between the inner and outer mitochondrial membranes.

proton pump

Explanation:

There are four major respiratory enzyme complexes that make the electron transport chain. These complexes are complex I, II, III, IV. All these complexes collectively act as proton pump and remove the H+ from the matrix o mitochondria and pump it into intermembrane space against the concentration gradient.

This generated an electrochemical gradient between the mitochondrial matrix and intermembrane space. So when these H+ comes back in the mitochondrial matrix through ATP synthase it generates ATP from ADP. Therefore the correct answer is a proton pump.