The oxidation of SO2 to SO3 is catalyzed by NO2. The reaction proceeds according to: NO2(g) +

Question:

The oxidation of SO2 to SO3 is catalyzed by NO2. The reaction proceeds according to:
NO2(g) + SO2(g) → NO(g) + SO3(g)
2 NO(g) + O2(g) → 2 NO2(g)
(a) Show that the two reactions can be summed to give the overall oxidation of SO2 by O2 to give SO3.
(b) Why do we consider NO2 a catalyst and not an intermediate in this reaction?
(c) Is this an example of homogeneous catalysis or heterogeneous catalysis?