Redox Reactions...

Statement I : The oxidation state of Cr in $$Al_2(Cr_2O_7)_3$$ is +3.
Statement II : as a neutral compound, the sum of oxidation numbers of all the atoms must equal zero.

In which of the following does sulphur has the lowest oxidation state? 

What is the oxidation number of $$Mn$$ in $$Mn{O}_{2}$$?

What is the oxidation number of $$Si$$ in the compound $$CaSi{O}_{3}$$?

What is the oxidation number of lead in $$Pb{F}_{2}$$?

In which substance does manganese have the highest oxidation number?

Which of the following are redox reactions?
I. $$PCl_{3} + Cl_{2}\rightarrow PCl_{5}$$
II. $$Cu + 2AgNO_{3} \rightarrow Cu(NO_{3})_{2} + 2Ag$$
III. $$CO_{2} + 2LiOH \rightarrow Li_{2}CO_{3} + H_{2}O$$
IV. $$FeCl_{2} + 2NaOH \rightarrow Fe(OH)_{2} + 2NaCl$$

The oxidation number of chromium in $$K_{2}CrO_{4}$$ is?

What is one of the spectator ions in the following reaction?
$$Pb(NO_{3})_{2} (aq) + 2KI(aq) \rightarrow PbI_{2} (s) + 2KNO_{3}(aq)$$

Which of the following reactions represents an oxidation-reduction reaction?