The correct option is Ionosphere.
Explanation
The internal structure of the Earth is divided into concentric layers based on chemical composition and physical properties. The three primary compositional layers are the Crust, the Mantle, and the Core.
Detailed Analysis:
- Crust: This is the outermost solid part of the Earth. It is brittle in nature and varies in thickness between continental and oceanic areas. It is a compositional layer of the Earth's interior.
- Mantle: Situated beneath the crust, the mantle extends to a depth of approximately 2,900 km. It constitutes the bulk of Earth's volume and mass. It is a compositional layer of the Earth's interior.
- Outer Core: The core is divided into the liquid Outer Core and the solid Inner Core. The Outer Core is responsible for Earth's magnetic field. It is a compositional layer of the Earth's interior.
- Ionosphere: This is a layer of the Earth's atmosphere, not the interior. It contains ionized air and is located within the thermosphere, extending from about 60 km to 1,000 km above the Earth's surface.
Key Takeaway:
The Earth's interior comprises the Crust, Mantle, and Core. The Ionosphere is a functional layer of the upper atmosphere associated with radio wave propagation.