Okay, so my class is getting ready for finals, and in doing so, we're working on chapter tests that we never did earlier in the year. The big problem is that we've never learned some of the stuff the tests are over. So, can anyone please explain to me net ionic equations and oxidation numbers? Please? My book doesn't really explain this at all, and the little bit it does makes no sense. I've included a few example questions with with I think are the correct answers. If you see that they are wrong, could you please tell me and explain why they are wrong and how to find the correct ones? Thank you so much!

1) When aqueous solutions of AgNO3 and KI are mixed, AgI precipitates. What is the balanced net ionic equation?
A: I think it's Ag+ (aq) + I- (aq) -> AgI (s).
If I understand this a little bit, to find the ionic equation you have to find the spectator ions and get rid of them. However, I'm not always sure how to get the spectator ions.

2) In which reaction does the oxidation number of oxygen increase?
a. Ba(NO3)2 (aq) + K2SO4 (aq) -> BaSO4 (s) + 2 KNO3 (aq)
b. HCl (aq) + NaOH (aq) -> NaCl (aq) + H2O
c. *I think this is the answer* MgO (s) + H2O (l) -> Mg(OH)2 (s)
d. 2 SO2 (g) + O2 -> 2SO3 (g)
e. 2H2O (l) -> 2H2 (g) + O2.

3) Which of the following is an oxidation-reduction reaction?
a. Cu (s) + 2AgNO3 (aq) -> 2Ag (s) + Cu(NO3)2 (aq)
b. *I think this is the answer* HCl (aq) + NaOH (aq) -> H2O (l) + NaCl (aq)
c. AgNO3 (aq) + HCl (aq) -> AgCl (s) + HNO3 (aq)
d. Ba(C2H3O2)2 (aq) + Na2SO4 (aq) -> BaSO4 + 2NaC2H3O2 (aq)
e. H2CO3 (aq) + Ca(NO3)2 (aq) -> 2HNO3 (aq) + CaCO3 (s)

If you can help me at all, I would greatly appreciate it!