When a person breaths, his lungs can hold up to 5.5 Litre of air at body temperature `37^(@)C` and atmospheric pressure `("1 atm = 101 kPa")`. This Air contains `21%` oxygen. Calculate the number of oxygen molecules in the lungs.

Explanation

We can treat the air inside the lungs as an ideal gas. To find the number of molecules, we can use the ideal gas law.
`PV=NkT`
Here volume is given in the Litre. 1 Litre is volume occupied by a cube of side 10 cm.
`"1 Litre"=10cmxx10cm xx10cm=10^(-3)m^(3)`
`N=(PV)/(kT)=(1.01xx10^(5)xx5.5xx10^(-3))/(1.38xx10^(-23)xx310)=1.29xx10^(23)" Molecules"`
Only `21%` of N are oxygen. The total number of oxygen molecules
`=1.29xx10^(23)xx(21)/(100)`
Number of oxygen molecules `=2.7xx10^(22)` molecules