In which one of the following reactions is deltaH rxn equal to deltaH f of the product?

In which one of the following reactions is deltaH rxn equal to deltaH f of the product? Please show how you identified the 4 wrong answers. Note - no numbers needed, this problem must be answered without per instructor's instructions. I am just now sure how to do it by sight alone? Please tell me how you arrived at your answer.

1. F2(g) + H2(g) --> 2HF(g)

2. Mg(g) + O2(g) --> 2MgO(g)

3. NO2(g) + O(g) --> NO3(g)

4. SO3(g) + H2O(g) --> H2SO4(g)

5. S + O2 --> SO2 {note this formula did not come with type, e.g., g, s, l.}