Reduction or Oxidation in following reactions?

Just for a check i want conformation on each reaction is there oxidation or reduction occuring, state with a reason please.
1) Zn to Zn 2+ (This is a ion)
2) Mn2+ to MnO4 - (the 4 is the number of oxygens and - is the charge)
3) CO to CO2
4) CrO4 2- to Cr2O7 2- (the 4 and 7 are the number of oxygnes and the 2- is the charge)
5) NO2 to N2O4

Thanks

Answer:
well, basically all have an oxidation number. you much find this for the first compound/molecule, then find the oxidation number of the second compound/molecule and look how it changes. if the oxidation number increases then its oxidation, if the oxidation number decreases then its reduction

Here are some rules to finding oxidation numbers (from wikipedia)

All species in their elemental form are given the oxidation number of zero.

All monoatomic ions have the same oxidation number as the charge on the ion. e.g. Mg2+ has the oxidation number of +2.

All combined hydrogen has an oxidation number of +1 (except metal hydrides where its oxidation number is -1).

All combined oxygen has an oxidation number of -2 (except peroxides where the oxidation number is -1, and compounds with fluorine where it can be positive).

In polyatomic species, the sum of the oxidation numbers of the element in the ion equals the charge on that species (we can use this to find the oxidation number of elements in polyatomic species).

Group 1 elements such as K and Na and Group 2 elements such as Mg always have a +1 and +2 oxidation state in compounds, respectively.

Cl has a range of oxidation states when bonded to O. However, its oxidation number is always -1 when bonded to ionic compounds.

These are half-reactions

Zn >> Zn2+ Zn goes from 0 to + 2 oxidation

Mn2+ >> MnO4- Mn goes from +2 to +7 oxidation

CO >> CO2 C goes from +2 to + 4 oxidation

CrO42- >> Cr2O72- Cr goes from +6 to +6 no oxidation or reduction occurred

NO2 >> N2O4 N goes from +4 to +4

Zn is oxidized from zero to +2

Mn is oxidized from +2 to +7

C is oxidized from +2 to +4

Cr is +6 in both ions, so no change there.

N is +4 in both molecules, so no change there.

1, 2 and 3 are redox, but 4 and 5 are not.

1, 2 and 3 are all oxidation (electron loss).

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Reduction or Oxidation in following reactions?

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