Question

Which part of Earth is solid and extremely hot

Answer 1

Outer Core (Crust) is the liquid layer of the Earth {It's made of a mixture of iron and Nickle, which goes 7200 or 9000 degrees} ; Inner Core (Crust) is the solid layer of the Earth

So, for the Solid part it is Outer Core; but for the "extremely hot" is the Inner Core .

But, I would say the Inner Core would most likely be your answer