Question

multiple - choice question
the disappearance of s - waves at the mantle - outer core boundary shows
the inner core is solid
the mantle is liquid
the outer core is solid
the outer core is liquid
rewatch

Explanation:

S - waves (secondary waves) are shear waves that cannot travel through liquid. Since S - waves disappear at the mantle - outer core boundary, it implies that the outer core is liquid as S - waves cannot propagate through it. The mantle is solid (semi - solid in some regions due to plasticity but not liquid in the sense that S - waves can pass through it). The inner core being solid is not directly related to the disappearance of S - waves at the mantle - outer core boundary. And if the outer core were solid, S - waves would pass through it.

Answer:

the outer core is liquid