| Most common ion | Reductant strength |
| F– (fluoride) | very weak moderate |
| Cl– (chloride) | |
| Br– (bromide) | |
| I– (iodide) |
2X– + oxidant 
X2 + product arising from oxidant
The product arising from the oxidant will have one of its atoms in a more negative oxidation state due to accepting electrons.
Thus if a halogen is the oxidant, the product is the corresponding halide ion.
2I– + Cl2 I2 + 2Cl–
It is easy to predict the product arising from the oxidant in this case as halogens only have one negative oxidation state (X–).
X2 + product arising from oxidantThe product arising from the oxidant will have one of its atoms in a more negative oxidation state due to accepting electrons.
Thus if a halogen is the oxidant, the product is the corresponding halide ion.
2I– + Cl2
I2 + 2Cl–It is easy to predict the product arising from the oxidant in this case as halogens only have one negative oxidation state (X–).
| sulfur species | Oxidation number(S) |
| H2SO4, SO3, SO42–, HSO4– | +6 |
| SO2 | +4 |
| S | 0 |
| H2S | -2 |
H2SO4 + reductant product(s) arising from reductant + product(s) arising from oxidant
If the reductant is a halide ion, the product arising from it will be a halogen (X2)
H2SO4 + 2X– X2 + product(s) arising from oxidant
As seen in the table at the right, the product arising from S(+6) in H2SO4 accepting electrons is not so easy to predict because there are several oxidation states of sulfur below +6. This product could be SO2, S or H2S, but it most certainly is not SO3, SO42–, or HSO4–.
product(s) arising from reductant + product(s) arising from oxidantIf the reductant is a halide ion, the product arising from it will be a halogen (X2)
H2SO4 + 2X–
X2 + product(s) arising from oxidantAs seen in the table at the right, the product arising from S(+6) in H2SO4 accepting electrons is not so easy to predict because there are several oxidation states of sulfur below +6. This product could be SO2, S or H2S, but it most certainly is not SO3, SO42–, or HSO4–.