# How many moles are in 4.21 x 10^22 molecules of SO_3?

Well a molar quantity specifies $6.022 \times {10}^{23}$ individual items of stuff..........
$\left(4.21 \times {10}^{22} \cdot \text{molecules")/(6.022xx10^23*"molecules} \cdot m o {l}^{-} 1\right)$
$= 0.0700 \cdot m o l$, and thus there $0.0700$ moles of $S {O}_{3}$, $0.0700$ moles of $\text{S atoms}$, and $0.210$ moles of $\text{oxygen atoms}$.