The upper atmosphere layer is known as

Options

A. troposphere
B. mesosphere
C. ionosphere
D. chromosphere

Answer

To determine what the upper atmosphere layer is known as, we can analyze the different layers of the atmosphere based on their altitudes and characteristics.

### Step-by-step Solution:

1. **Identify the Layers of the Atmosphere**:
- The atmosphere is divided into several layers based on altitude. The main layers include:
- Troposphere
- Stratosphere
- Mesosphere
- Ionosphere

2. **Define Each Layer**:
- **Troposphere**: This is the lowest layer of the atmosphere, extending from the Earth's surface up to about 18-20 km. It is where weather occurs.
- **Stratosphere**: This layer is above the troposphere, extending from about 20 km to 50 km. It contains the ozone layer.
- **Mesosphere**: This layer is above the stratosphere, extending from about 50 km to 90 km. It is where most meteors burn up upon entering the Earth's atmosphere.
- **Ionosphere**: This is the uppermost layer of the atmosphere, extending from about 90 km to approximately 400 km. It is characterized by the presence of ions and free electrons, which can reflect radio waves.

3. **Determine the Upper Atmosphere Layer**:
- Among the layers mentioned, the uppermost layer is the **Ionosphere**. It is located at the highest altitude compared to the other layers.

4. **Select the Correct Option**:
- Given the options:
- A) Troposphere
- B) Mesosphere
- C) Ionosphere
- D) Chromosphere
- The correct answer is **C) Ionosphere**.

### Final Answer:
The upper atmosphere layer is known as the **Ionosphere**.

---