The correct statement is: "The mantle is both solid and liquid, while the inner core is entirely solid."
To clarify:
- The Earth's mantle is mostly solid but behaves like a viscous fluid over geological timescales, allowing for convection and the circulation of material.
- The inner core is solid and primarily composed of iron and nickel, despite being at extremely high temperatures.
Therefore, the mantle being both solid and liquid, and the inner core being entirely solid is the accurate description.