Final answer:
Glaciers and ice sheets contain the largest fraction of Earth's freshwater within the hydrosphere, but groundwater represents the largest reservoir of usable freshwater.
Step-by-step explanation:
The reservoir of the hydrosphere that has the largest fraction of Earth's liquid freshwater is glaciers and ice sheets. While groundwater represents the largest reservoir of usable freshwater, glaciers and ice sheets contain the most total freshwater. However, most of this freshwater is not easily accessible for human use, as it is trapped in the form of ice in areas such as Antarctica and Greenland. Comparatively, rivers, lakes, and soil moisture contain much smaller amounts of freshwater.