Answer
See explanation below
Work Step by Step
a) Differentiation is the process of formation of Earth into regions (core, mantle, and crust) of differing compositions. Substances separated according to their densities (think like a centrifuge), with denser material in the core and the less dense material in the crust.
(b) O, Si, Al, and Fe (Refer to data below)
(c) Oxygen is present in both those places but not the core.
