CO_{2} has 44 g/mole (Atomic weight of carbon atom = 12, that of oxygen atom = 16)

Avogadro's number is 6.0221415*10^{23} molecules/mole

so there are (13.2/44)*6.0221415*10^{23} molecules in 13.2 g of CO_{2}

$${\frac{{\mathtt{13.2}}}{{\mathtt{44}}}}{\mathtt{\,\times\,}}{\mathtt{6.022\: \!141\: \!5}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{{\mathtt{23}}} = {\mathtt{180\,664\,245\,000\,000\,000\,000\,000}}$$

or 1.80664245*10^{23} in total.

In each of these molecules there are two oxygen atoms, so double this.

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