Molar mass of sulphur dioxide ( SO2) = 64.066 g/mol
Molar mass of water ( H2O ) = 18.0 g/mol
process:
2 H2S + 3 O2 --> 2 H2O + 2 SO2
2 * 18 g H2O --------------> 2* 64.066 g SO2
72.0 g H2O ----------------> mass of SO2
mass of SO2 = 72.0 * 2 * 64.066 / 2 * 18
mass of SO2 = 9225.504 / 36
mass of SO2 = 256.264 g
1 mole --------------> 64.066 g
mole SO2 ----------> 256.264
mole SO2 = 256.264 / 64.066
= 4 moles of SO2
hope this helps!.
