Pitanje iz fizike

Pisao sam na nekom stranom forumu, zato je na engleskom, pretpostavljam da nije problem.

Back in class we had the following problem:

The air we breathe is about 21% oxygen, by volume. Exhaled air contains about 14% of oxygen. The absorption of oxygen within the lungs takes place in tiny spherical compartments called alveoli which have a diameter of the order of 0.1 mm. Estimate the number of oxygen molecules absorbed in one breath in each of the alveoli. (Assume that body temperature is 37°C.)

$n= \frac{pV}{RT}$ $= \frac{101325 Jm^{-3}\times 5.23\times 10^{-13}m^{3}}{8.3145JK^{-1}mol^{-1}\times 310.15K}$
$n=2.06\times 10^{-11} mol$
$N= 1.24\times 10^{-13} molecules$

I assumed that the pressure inside the alveoli is 1 atm, that $r= \frac{d}{2}$ and calculated the volume using $V= \frac{4}{3} r^{3} \pi$

Now, $7 \% \times N= 8.7 \times 10^{11}$ and End-of-chapter solution is $6.9 \times 10^{12}molecules$

What am I doing wrong?

Dakle, u čemu je problem?

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