# At STP, how many molecules of SO_2 are in 0.400 L of SO_2?

$= 0.1075 \cdot {10}^{23}$ molecules of $S {O}_{2}$
We know1 mole or $6.022 \cdot {10}^{23}$ molecules of $S {O}_{2}$ occupies 22.4 L at STP
So at STP 1L will contains $\frac{6.022}{22.4} \cdot {10}^{23}$ molecules of $S {O}_{2}$
$\therefore$At STP 0.4L will contains $\frac{6.022}{22.4} \cdot 0.4 \cdot {10}^{23} = 0.1075 \cdot {10}^{23}$ molecules of $S {O}_{2}$