n factor or valency factor
n factor or valency factor is a term used in redox reactions. It is used to describe the number of electrons gained or lost per atom during a reaction.
Zn(s)+CuSO4(aq)⟶ZnSO4(aq)+Cu(s)
Here Zn loses two electrons to become Zn+2 . So the n factor for zinc is 2
6FeSO4+K2Cr2O7+7H2SO4⟶3Fe2(SO4)3+K2SO4+Cr2(SO4)3+7H2O
The Fe+2 is oxidized to Fe+3 by losing one electron. So the n factor for FeSO4 is 1
COOH−COOH⟶2CO2+2H++2e−
In oxalic acid, the number of replaceable hydrogen ions is 2, hence the n factor is 2.