Which of the following statements about the atmosphere is correct?
1. Troposphere is the lowest layer of the atmosphere.
2. Ionosphere lies above the mesosphere.

The correct answer is Both 1 and 2.

Let us analyze each statement step-by-step to understand the structure of Earth's atmosphere:

Statement 1: Troposphere is the lowest layer of the atmosphere.
This statement is correct. The troposphere is the innermost and lowest layer of Earth's atmosphere. It extends from the Earth's surface up to an average height of about 8 to 15 kilometers (depending on latitude). Almost all weather phenomena, such as clouds, rain, and snow, occur within this layer.

Statement 2: Ionosphere lies above the mesosphere.
This statement is also correct. The layers of the atmosphere from lowest to highest are:
1. Troposphere
2. Stratosphere
3. Mesosphere
4. Thermosphere (which contains the Ionosphere)
5. Exosphere
The ionosphere is an electrically charged region located within the thermosphere, directly above the mesosphere (roughly extending from 80 km to 600 km above the surface). It plays a key role in radio communication by reflecting radio waves back to Earth.

Since both Statement 1 and Statement 2 are accurate, the correct choice is Both 1 and 2.