Given below are two statements: One is labelled as Assertion (A) and the other is labelled as Reason (R):
Assertion (A): The average composition of atmosphere near the surface of earth is given on dry basis and in terms of mixing ratio (weight percent basis).
Reasons (R): Water content in atmosphere near the surface of the earth is variable with respect to location, time and the concentration of gases in volumetric units (moles/litre) varies with temperature and pressure conditions.
In the light of the above Statements, choose the correct answer from the options given below: