(a) (i) Air : Absence of trees will lead to increased CO2 which leads to global warming.
(ii) Soil: Roots bind the soil. Reduction in forest cover will lead to soil erosion by U winds, floods.
(iii) Water: The roots of trees enhance the water holding capacity of the soil.
No life exists on them.
So, CO2 is the major component of atmosphere on Venus and Mars.