Answer Happy

Hello, I have a question about the chemistry problem : Redo
reaction, can you help me for four questions and can you
please show me the steps that I can understand quickly? Thanks a
lot!
H2C2O4 +
H3O+ + MnO4- ------> Co2 +
Mn2+ + H2O (here i need to find
the ON, but
SO32- + Ni(OH)3-1
-----> Ni + SO42- (but here I
do not need to find the ON,
Cl- + H3O+ + NO3-
-------> NO + H2O + Cl2 (here
I need to find the ON, but
I- +
ClO3-1 -----> I3-1 +
Cl- (but here I do not need to find
the ON.....
Is it possible to explain to me when I have to find the
oxidation number and when I do not need to find the oxidation
number?)