Classify the following reactions as either synthesis or decomposition:

1) SO3 (g) + H2O (l) → H2SO4 (aq)

2) NH4NO3 (s) → N2O (g) + 2 H2O (g)

3) A + B → C

4) 2 H2O → 2 H2 + O2

5) 3 Fe (s) + O2 (g)→ Fe2O3 (s)

6) C → A + B