我想問下係咪所有化學elements個oxidizing no.未到盡的(eg.Fe2+),佢就係reducing agent;而個oxidizing no.到左盡(eg.Fe3+)就係oxidizing agent? 好似聽唔知邊個講過,唔係好記得!

Not really. It depends on how easily the oxidation state of an element changes. This tendency is quantified by the standard reduction potential of the element (or ions in various oxidation states). Rhenium is a good example since it has a wide range of oxidation states (0,III,IV,VI,VII). The intermediate species, such as Re(III), can be either oxidizing or reducing agent since the standard reduction potentials for Re(VI) ---> Re(III) and Re(III) ---> Re(0) are not large (~0.3eV), and can easily be overcome.

Certainly if an element already attains its highest oxidation state, then it cannot be further oxidized. In other words, it must be either oxidizing (to gain electrons) or nothing. So do the species in their lowest oxidation states; they can be either reducing (to give up electrons) or nothing.

Not really. It depends on how easily the oxidation state of an element changes. This tendency is quantified by the standard reduction potential of the element (or ions in various oxidation states). Rhenium is a good example since it has a wide range of oxidation states (0,III,IV,VI,VII). The intermediate species, such as Re(III), can be either oxidizing or reducing agent since the standard reduction potentials for Re(VI) ---> Re(III) and Re(III) ---> Re are not large (~0.3eV), and can easily be overcome.

Certainly if an element already attains its highest oxidation state, then it cannot be further oxidized. In other words, it must be either oxidizing (to gain electrons) or nothing. So do the species in their lowest oxidation states; they can be either reducing (to give up electrons) or nothing.