What mass of sulphur must be burned to produce 64.0 tonnes of sulphur dioxide.

Question

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So far, I have calculated the molecular mass of SO2( 64.1 ) . and then found out the number of moles of sulphur dioxide. ( 998.4) What to do now?

Answer 1

I don't know how you obtained 998.4 mols. I might believe 0.9984.
If you want the answer in tonnes, I would do this. A little unconventional but it saves a lot of work. If we work in tonnes, we never convert 64.0 tonnes to grams. Then we don't need to convert grams back into tonnes. I'm going with the molar mass SO2 as 64

S + O2 ==> SO2
64.0 tonnes SO2 needed/64 = 1 mol (technically, this is not 1 mol but 1 tonne-mol but if we keep our units the same that will be ok).
1 tonne mol SO2 needed means we must start with 1 tonne mol S to get there (the equation tells you it is 1 SO2 for 1 S).
1 tonne mol S x 32 = 32 tonnes S. You can change that to grams if needed.

Answer 2

the 64 is a good clue

the mass ratio of the components is constant

amu, or grams, or tonnes
... same ratio