The correct answer is nickel and iron. Explanation & Key Takeaways: Core: • The innermost layer is the core with a radius of about 3500 km. • The central core has a very high temperature and pressure. • The inner core (1200 km) is in the solid state whereas the outer core (2300 km) is in the liquid state. • The innermost layer is the core with a radius of about 3500 km and divided into Inner and Outer core. • The inner core is with a radius of 350 km mainly made up of- nickel and iron. The innermost layer is also called ‘nife’ (ni - nickel and fe - ferrous- iron). Related Concepts: The Earth is divided into four main layers: the solid crust on the outside, the mantle, the outer core, and the inner core. • All those layers are separated from each other through a transition zone. • These transition zones are called discontinuities. • Conrad Discontinuity: It lies between the Upper crust and Lower crust. • Mohorovicic Discontinuity: It lies between crust and mantle. • Repiti Discontinuity: It lies between the Upper mantle and Lower mantle. • Gutenberg Discontinuity: It lies between core and mantle. • Lehman Discontinuity: It lies between the upper core and lower core. Interior of the Earth: Crust: • The uppermost layer over the earth’s surface is called the crust. • It is the thinnest of all the layers. • on the continental masses, It is about 35 km and on the ocean floors, only 5 km. • The crust is the thinnest layer of the Earth and it amounts to less than 1% of our planet's volume. • The earth is made up of several concentric layers with one inside another, just like an onion. • The crust is the outermost layer of Earth and is made up of igneous, metamorphic, and sedimentary rocks. • The Earth's crust is unstable because of the exogenic forces. Mantle: • The Mantle extends up to a depth of 2900 km below the crust. • It is the widest section of the Earth.