Question

how many molecules is 415 L sulfur dioxide a STP

Answer 1

At STP, 1 mole of any gas occupies 22.4 L.

Therefore,

$n_{SO_2}=\frac{415L}{22.4L/mol}=18.5mol$

Number of molecules equals $18.5mol\times6.022\cdot10^{23}=1.11\cdot10^{25}$

Answer: $1.11\cdot10^{25}$