Final answer:
As one descends from the Earth's mantle to the core, both the density and temperature increase, with the core being largely composed of iron, nickel, and sulfur at a very high density.
Step-by-step explanation:
As you move downward into the Earth, from the mantle to the core, you will observe several changes: both the density and temperature increase. The mantle's density increases from about 3.5 g/cm³ to more than 5 g/cm³ due to compression by the weight of the overlying material. In contrast, the Earth's core is even denser and hotter, with the outer core being liquid and the inner core being solid due to the extreme pressure. The core is composed mainly of iron, along with nickel and sulfur, and has a high density resulting from this incredible pressure. Additionally, the temperature of the core reaches around 2,500°C, much hotter than the mantle. Hence, the correct option is (b) Both the density and temperature increase.