Due to differentiation which part developed at Earth's centre?

Correct answer: Core

The governing concept is planetary differentiation. When the early Earth became sufficiently hot and partly molten, materials separated according to density. Heavy elements and substances, especially iron and nickel, moved downward under gravity and concentrated at the centre, forming the core. Lighter silicate materials remained above them and contributed to the mantle and crust. Therefore option A, the core, is correct. The atmosphere is an outer gaseous layer, not a central differentiated part. Oceans occupy surface depressions and formed much later as water accumulated, while a mountain peak is a surface landform produced by geological processes. These alternatives do not result from the sinking of dense material during differentiation. The answer follows directly from the relationship between density, gravity, and Earth’s internal structure.