Answer:
B. 2.9X10^21
Explanation:
The volume of air inside a breath is
[tex]V=6.0\cdot 10^{-4} m^3[/tex]
Of this, only 20% is oxygen, so the volume of oxygen is
[tex]V=(0.20)(6.0\cdot 10^{-4}m^3)=1.2\cdot 10^{-4}m^3[/tex]
Then we can find the number of moles of oxygen by using the ideal gas equation
[tex]pV=nRT[/tex]
where we have
[tex]p=1.0\cdot 10^5 Pa[/tex] is the gas pressure
[tex]V=1.2\cdot 10^{-4}m^3[/tex] is the oxygen volume
n is the number of moles of oxygen
[tex]R=8.314 J/mol K[/tex] is the gas constant
T = 300 K is the temperature
Solving for n, we find
[tex]n=\frac{pV}{RT}=\frac{(1.0\cdot 10^5 Pa)(1.2\cdot 10^{-4}m^3)}{(8.314 J/mol K)(300 K)}=4.8\cdot 10^{-3} mol[/tex]
Since the number of molecules in 1 mol is
[tex]N_A = 6.022\cdot 10^{23}[/tex] (Avogadro number)
Then the number fo molecules in [tex]4.8\cdot 10^{-3} mol[/tex] of oxygen is
[tex]N = nN_A = (4.8\cdot 10^{-3}mol)(6.022\cdot 10^{23})=2.9\cdot 10^{21}[/tex]
