Question

inge lehmann noticed that seismic waves bounced back to the surface helping show that the inner core of the earth is...
molten.
liquid.
hollow.
solid.

Explanation:

Inge Lehmann's work with seismic waves showed that the Earth's inner core is solid. Seismic waves (specifically P - waves and S - waves) behave differently in solid and liquid materials. S - waves cannot travel through liquid, but the behavior of waves in the inner core indicated a solid structure. The other options: molten and liquid are incorrect as the outer core is liquid, and hollow is not a valid description of the inner core's state.

Answer:

D. solid.