Which layer of earth is liquid?
oa) crust
ob) inner core
o c) outer core
od) lower mantle

The outer core is the liquid portion of the layers of the earth.

Outer core :)

I did some research and this is what I found. Hope it helps!

The only major layer of the earth that's liquid is the outter core, which is basically metal with the same composition of the inner core (mainly nickel and iron) but molten instead of solid. All the other major layers above and below it are though to be solid.

Because a model would make the investigation easier to understand