Question

(give scientific reason) at dawn, in winter, we see dew drops on leaves of trees

Answer 1

we know that some water is present in our environment in the form of water vapours. and at the time of dawn temperature falls down and water vapours got cooled and convert in the form of water droplets . and get collected on leaves.

Answer 2

Air has the capacity to retain water molecules as per its temperature. Generally, the higher the temperature the higher is the capacity of water to hold  molecules. there occurs a temperature where no more water molecule can be retained when the volume of air is cooled. Hence, it starts to condense into liquid water or ice. If condensation takes place above 0 C its called as dew. It especially occurs in winters because the air temperature is low and it grows diminished further as the sun decreases ending in Air not capable to retain the water more than its capacity.