Question

how to find the oxidation number for a half reaction?

Answer 1

have you got a specific example you can work from?

a half-reaction will show you the oxidation numbers of the reactants and products of hte half-reaction, like this:

\[Mg^{+2} + 2e^{-1} \rightarrow Mg^0\]\[Cl_2^0 + 2e^{-1} \rightarrow 2Cl^{-1}\]each half-reaction shows what the oxidation numbers (charges) of each species is before and after the reaction. A table of half-reactions will have dozens more, but they will all look almost identical in their formats