which gradient refers to the difference across a membrane due to both a chemical force and an electrical…

Brief Explanations:

The electrochemical gradient takes into account both the chemical concentration difference and the electrical potential difference across a membrane. A concentration gradient only considers the difference in solute concentration. A chemiosmotic gradient is related to the movement of protons in the context of ATP - synthesis. The electrochemical gradient combines chemical and electrical forces.

Answer:

C. electrochemical