Which factor would not influence the diffusion coefficient in a liquid?

• A. Temperature
• B. Viscosity
• C. Activation energy
• D. Molecular size

Answer: (C)

The diffusion coefficient in a liquid reflects how easily particles move through the medium. It rises with higher temperature because molecules have more kinetic energy and explore space faster. It falls with greater viscosity since a thicker fluid offers more resistance to motion. It also decreases with larger molecular size because bigger particles experience more drag as they move through the solvent. Activation energy, while it features in the temperature dependence of diffusion, is not a direct knob you adjust to set D at a given temperature; it describes the energy barrier of the diffusion process and determines how sensitive D is to temperature. At a fixed temperature, Ea doesn’t independently set the diffusion rate, so it’s not a direct influence in the same sense as temperature, viscosity, or molecular size.