Final answer:
Larger ions have higher conductance and mobility as they experience fewer solvation interactions with solvent molecules due to lower charge density, allowing them to move more freely and contribute to higher conductivity.
Step-by-step explanation:
The question asks why larger ions have higher conductance and mobility. The correct explanation for the observed higher conductance and mobility of larger ions compared to smaller ions is related to the number of interactions they have with solvent molecules and their charge density. Larger ions generally have lower charge density and, as a result, fewer solvation interactions with the solvent molecules, which reduces the resistance they encounter as they move through the solution. This allows them to move more freely, leading to greater conductivity and mobility.
Smaller ions, on the other hand, typically have higher charge densities and form stronger solvation shells. This results in a higher frequency of collisions with solvent molecules, which increases resistance and reduces mobility. This concept is supported by the general observation that conductivity of electrolyte solutions is affected by the movement of ions—more free-moving ions result in better conductivity.