The density of liquid water (1g/mL) is more than that of ice (0.92g/mL) due to lesser magnitude of intermolecular dhdrogen bonding and lesser intermolecular spaces. Therefore mobility of `H^(+)` ions in liqued water is expected to be less. Moreover, `H^(+)` ions get hydrated and becomes heavier in liquid water as compared to ice (solid state). Consequently, their mobility in water is less.
