# 39 x 10^22 molecules of CO_2 is equal to how many moles of CO_2?

Well, one mole of molecules specifies $6.022 \times {10}^{23}$ individual molecules........and we get a bit over a half a mole of molecules.
You have $3.90 \times {10}^{23}$ molecules, and the molar quantity is the simply the quotient,
$\left(3.90 \times {10}^{23} \cdot \text{molecules")/(6.022xx10^23*"molecules} \cdot m o {l}^{-} 1\right)$ $=$ ??mol