Question

What is the mass of a cubic meter of air at 20oC at sea level?

Answer 1

The density of air at $20^\circ \rm C$ at sea level is equal $\rho=\rm 1.2\: kg/m^3$. Hence, the mass of a cubic meter of air

$$m=\rho V=\rm 1.2\: kg/m^3*1\: m^3=1.2\: kg$$