Use the ΔH°f and ΔH°rxn information provided to calculate ΔH°f for SO3(g):
It’ts just products minus reactants.
therefore Hrxn= 2(SO3)- [2(-297) + 1(0)]
the Hrxn is given and the value of O2 is 0 because any element in it’s natural state is automatically 0.
Hopefully this helps.
I just did this problem lol