You can only ask one question at a time so I edited out your second question.
A: You have a mistake in your reaction. I suspect you mean:
2SO2 + O2 --> 2SO3
The SO2 has the S in the +4 oxidation state and O in the -2. The SO3 has the S in the +6 state and the O in the -2. So the sulfur goes from +4 to +6. In other words, it loses two electrons and becomes oxidized. So this is a redox reaction (the oxygen is reduced).
B: The NO2 has the N in the +4 state and the O in the -2 state. The HNO3 has the N in the +5 state and the O in the -2 state (this gives the NO3- anion a total charge of -1). The NO has the N in the +2 state and the O in the -2 state. So two of the NO2 molecules are oxidized to HNO3 and one is reduced to NO. This is a redox reaction.
C: The SO2 has the S in the +4 state and the O in the -2 state. The H2SO3 has the S also in the +4 state since the SO3 anion must have a -2 charge. So nothing is oxidized, therefore it is not a redox reaction.