The correct option is A Troposphere
Troposphere
is considered as the most important layer of atmosphere. It is the lower most
layer of the Atmosphere. Its average height is 13 km. The thickness varies from
8 km to 18 km, with maximum at equator and minimum poles. All the atmospheric
phenomena such as rains, wind, clouds, etc. take place in this layer. Troposphere
contains roughly 80% of the mass of Earth's atmosphere and it composed of
composed of nitrogen (78%) and life giving gas oxygen (21%) with small
concentrations of other trace gases. Hence, Troposphere is very important for
the existence of life on earth as it causes the cloud formation, raining and
maintaining the heat balance of the earth.