Final answer:
Earth's core, which is mostly composed of iron and nickel, is the correct answer to the student's question, specifically the Earth's outer core (D) which is in a liquid state.
Step-by-step explanation:
The layer that is comprised primarily of iron (Fe) and nickel (Ni) is Earth's core. Our planet's core is divided into two parts: the inner core and the outer core. The inner core is a solid sphere composed of an iron and nickel alloy. Surrounding the solid inner core is the outer core, which is a shell of liquid iron and nickel. The fluid motion in the outer core is responsible for generating the Earth's magnetic field.
By comparison, the Earth's mantle, which lies above the core, is made of ultramafic rock that contains iron and magnesium but in smaller quantities compared to the core. The crust is the outermost layer of the Earth, which is predominantly composed of silicon oxides and aluminum oxides, and the crust is much less dense than the other layers. The correct answer to the question is D) Earth's outer core, as this is the layer made predominantly of a liquid mixture of Fe and Ni.