Question

if a potted plant is covered with a glass jar, water vapour appears on the wall of glass jar. why?

Answer 1

because of transpiration.
plants occur transpiration to loose excess water and also,reduce heat of the plant.

Answer 2

if we ported a plant which is covered by a glass jar then Water vapours appear on the wall of Glass jar because as water and the plant itself having some moisture inside it if there is not coming so through the process transpiration it loses water in the jar and water gets evaporated and it it becomes water vapour so it do not get place to go outside and it forms droplets on the glass jar