Thank you so much for the reply. I wanted to ask why don't we multiply enthalpy change for sulfurtrioxide with 2 .First of all reverse the first reaction and multiply it by 2 as we do in writing equations for contact process this will also change the sign of enthalpy change required for this reaction i.e 2(296.5)=+593 make an overall equation of the both equations given to get 2SO2(g) + O2(g) → 2SO3(g)
then
-791.4+593= -198.4 thus D is correct option.