Carbon dioxide makes up approximately 0.04% of earth's atmosphere. if you collect a 2.9 l sample from the atmosphere at sea level (1.00 atm) on a warm day (27 ∘c), how many co2 molecules are in your sample?

number of molecules=  2.83 x 10^19

Explanation:

0.04 % means 0.04 L CO_2 in 100 L atmosphere

so for 2.9 L atmosphere CO2 vol = ( 0.04/100) x 2.9 = 0.00116

T = 27°C = 300 K , P = 1 atm ,

n = PV/RT = ( 1 x 0.00116) ÷ ( 0.08206x300) = 4.71×10^{-5}

number of molecules = 6.023 x 10^23 x 4.71×10^{-5}   = 2.83 x 10^19

the answer is b, have negligible mass