Question

How many molecules do CO2 are present in one litre bottle air containing 0.03% volume of CO2 at STP.

Answer 1

1mole of any substance contains 22.4litres of amount. so in 1litre CO2 contains 1/22.4 moles.
also in 0.03% of 1litre of CO2 contains
1/22.4×0.03=0.00133 moles. so the no. of molecules=6.022×10²³×0.00133=0.0080×10²³.

Answer 2

The number of molecules of $\bold{CO_2}$ is $\bold{8.065 \times 10^{18}}$

Explanation:

Air volume is 0.03% means 100 parts per volume of air contain 0.03% parts per volume of $CO_2$.  

One liter of air will therefore contain 0.0003 liters of $CO_2$.

We know that,

There is one mole of $CO_2$ in NTP 22.4 liters of $CO_2$ and $6.022 \times 10^{23}$ number of molecules.

So, 0.0003 liters of $CO_2$ will contain $\frac{0.0003}{22.4}$ moles of $CO_2$

$\Rightarrow\left(3 \times 10^{-4}\right) \times\left(\frac{6.022 \times 10^{23}}{22.4}\right)$

$\therefore \text { Number of molecules }=8.065 \times 10^{18}$