Hint: We all know that dew is water which is in the form of droplets, and appears on thin exposed objects in the morning or evening. To know the reason behind the formation of dew we need to examine the processes which are present as options.
Step by step answer:
Dew forms in the morning on leaves and grass because of the warmer deposit of water molecules by the process of cooling. This process is commonly called condensation.
Specifically, condensation is defined as the process where a material undergoes a change from a gaseous state to a liquid state. As the exposed surface cools by radiating its heat, atmospheric moisture condenses at a rate greater than that at which it can evaporate.
This results in the formation of water droplets. Therefore we can see that the correct answer is Option A.
Additional Information:
We cannot expect dew to form every day. However there are certain conditions under which dew form.
For instance if a warm clear day is followed by a cool air, evening dew will likely form. But on a normal warm day water evaporates from the warm ground into the air, so due formation is not likely to happen.
Note: We know that if an object becomes cool enough the air around the object will also cool down around the object.
Therefore colder air is able to hold less amount of water vapour as compared to warmer air. This is the main reason why water vapour in the air is forced to cool around the objects and so does the process of condensation takes place.
