Final answer:
The question refers to Earth's metallic core, containing dense elements like iron and nickel, with a radius of 3,400 km, and making up about 35% of Earth's mass, it's also the densest planetary body in our solar system.
Step-by-step explanation:
The dense metallic core at Earth's center is what the question refers to, which contains the densest elements, has a radius of about 3,400 km, and accounts for about 35% of Earth's mass. This core is composed primarily of iron and nickel and is divided into two parts: a liquid outer core and a solid inner core. The innermost part of the core is solid because of the immense pressures that exist at the center of the Earth.
Earth's core is extremely dense, with densities far exceeding the average density of bulk matter at the surface. This is similar to how protons and neutrons are densely packed in the atomic nucleus. The density of the core contributes significantly to Earth's overall density, making it the densest of the planets in our solar system.