Answer
1.96 x 10^19 molecules of CO2
Work Step by Step
We are given the volume (2L of sample), the pressure (1atm) and the temperature of the atmosphere (27C and then we add 273 to have 300K). We can then find the number of moles by using the ideal gas law:
PV = nRT so n = PV/RT = (1atm * 2L) / (0.0821 * 300K) = 0.0812 moles
Then to find the number of molecules, we multiply by Avogadro's number, 6.022 x 10^23, which gives 4.89 x 10^22 molecules.
Since the atmosphere is 0.04% of the atmosphere we take
4.89 x 10^22 * (0.04/100) = 1.96 x 10^19 molecules of CO2
