What area of the earth is comprised mainly of extremely hot liquid metals

Out of the layers of the earth (the crust, the mantle, and the core), the core would be the answer to your question. More specifically, the outer core.

Both the inner and outer core is composed of mostly iron and nickel. Though the inner core would have the fact that it is hotter than the sun's surface, the composition of it is but of solid materials. This is due to pressure that renders the materials immovable. However, the outer core remains in the liquid form due to its relationship with the inner core. The heat from the inner core mobilizes the materials in the outer core and in the mantle. As the earth spins, the outer core's liquefied iron and nickel spins over the inner core which generates the magnetic field of the earth.