Concept:The troposphere is the atmospheric layer where weather processes, including cloud formation, occur.
Explanation:Rain clouds develop from water vapour that rises and cools.
This cooling happens mainly in the lowest atmospheric layer, the troposphere.
The troposphere contains most of the atmosphere’s water vapour and dust particles.
These particles act as nuclei around which cloud droplets form.
Higher layers like the stratosphere, mesosphere, thermosphere, and exosphere are too dry and stable for normal rain cloud development.
Therefore, the correct option is the troposphere.
Answer:D. Troposphere