If we assume the volume of every breath a person takes is 5.00x10^2 mL,?

Question

Calculate the number of molecules exhaled in each breath at body temperature, 37 degrees celcius and 1.0 atm.

Answer 1

PV=nRT
P= 1 atm
V= 0.5 L
T=310 K
R=0.082 (for units above)
solve for n and multiply by 6.02x10^23

Answer 2

This looks, to me, like a trick question. While it is easy to calculate how many moles of gas there are in 500 ml, the trick is that in the lungs, there are exchanges of oxygen for carbon dioxide. That varies from individual to individual.

To give the test writer the benefit of the doubt, you could do the above calculation, then adjust for variance from standard temperature and pressure using Boyle's Law.