Take an empty plastic bottle and put 5-10 ml water into it. Close the bottle tightly and shake it well. Place it under the sun for 10 minutes. Now, open the bottle and allow some smoke from an incense stick to enter it. Close the bottle tightly. Now, press the bottle with your hands for a few seconds and then release it.

Observation: When the bottle is placed in the sunlight, the water evaporates and water vapors saturate the air inside the bottle. When the bottle is pressed hard, the internal pressure becomes high and the air inside the bottle moves to a region of low pressure. The smoke particles act as nuclei to condense the water vapors into tiny droplets. When the pressure is released, the air inside the bottle becomes foggy; and when pressure is again applied, the fog disappears.

This occurs because the smoke particles of the incense stick act as nuclei for the water vapors to condense into droplets.