How can we find the average molecular weight of air from the mole basis of its major ingredients? 150 gram of solid sulphur (S) was required to burn in presence of 3.5 Kg of air. According to mole basis it was found that, 80% sulphur was converted to sulphur dioxide (SO2) and 10% was converted to sulphur trioxide (SO3). Find the average molecular weight of the outlet gas stream. You have to consider monoatomic sulphur.