1. a. Outer Core
The magnetic field of Earth is generated by the forces deep inside our planet. More specifically, it is the convection currents in the outer core layer that are managing to produce the magnetic field. These convection currents are made out of molten rock, and they are caused by the heat that is escaping the inner core and moves outwards toward the outer core. This process is called geodynamo, and its effects have big importance for the Earth and the living organisms on it, especially that the magnetic field of our planet also acts as a protector from the intense sun radiation.
2. d. Lithosphere
The only layer on Earth that can be described as brittle solid is the lithosphere. Unlike the layers that are deeper, the lithosphere is not as hot, nor has high pressure, so the rocks are in solid form, instead of being molten. This layer is also the smallest of all, and it is covering only the uppermost part of the planet. Apart from being the thinnest layer, it is also the layer that is composed of the lightest elements, as during the formation of Earth's layers, the heaviest elements were sinking to the center, while the lighter elements were pushed toward the surface.