The number of molecules present in 3 moles of ${\mathrm{CO}}_2 \mathrm{are}$

1 Mole of ${\mathrm{CO}}_2\to 6\times {10}^{23}(6.023\times {10}^{23}) \mathrm{molecules}$

$3 \mathrm{Moles} \mathrm{of} {\mathrm{CO}}_2 \to ? \mathrm{molecules} \mathrm{of} {\mathrm{CO}}_2$

 Then, number of molecules present in 3 mol ${\mathrm{CO}}_2 \mathrm{is}$ 

$\frac{3\times 6\times {10}^{23}}{1}=18\times {10}^{23}$