Final answer:
The sodium-proton exchanger is classified as an antiporter, which is a type of secondary active transporter that moves ions in opposite directions to maintain the cell's pH balance.
Step-by-step explanation:
The sodium-proton exchanger is an example of a B) antiporter. An antiporter is a type of secondary active transport system that transports substances in opposite directions across the cell membrane. Specifically, the sodium-hydrogen ion antiporter uses the energy from the influx of sodium ions, which have been built up outside the plasma membrane by primary active transport creating an electrochemical gradient, to move hydrogen ions (H+) out of the cell.
This mechanism is essential for maintaining the pH balance within the cell. It's important to note that although secondary active transport does not directly use ATP to function, it is still considered active because it relies on energy harnessed from the electrochemical gradient created by primary active transport processes, such as the sodium-potassium pump.