The correct answer is option 2: Troposphere. The troposphere is the lowest layer of the Earth`s atmosphere, extending from the surface up to about 12 kilometers (or 7.5 miles) in altitude. It is the layer in which most weather phenomena occur.

The troposphere is characterized by decreasing temperature with increasing altitude. This temperature gradient leads to the formation of various weather patterns, such as clouds, precipitation, and storms. The interaction between warm and cold air masses, as well as the presence of water vapor, is responsible for creating the dynamic weather conditions we experience on Earth.

It`s important to note that while the other options are also layers of the atmosphere, they do not play a significant role in weather phenomena. The ionosphere is responsible for auroras and radio wave propagation, while the stratosphere and tropopause have more limited roles in weather patterns.