Question

Elements in the same group in the periodic table exhibits same oxidation state. Is this statement true?

Answer 1

The Group number represents the MAXIMUM oxidation state observed for the element......the statement is neither true nor valid.

Explanation:

Take the halogens, for example.....These come from `"Group VII"` of the old Periodic Table. The maximum oxidation number of say chlorine is `+VII`, the which it expresses in `"perchlorate"`, `ClO_4^(-)`. Most of the time, however, we find chlorine as its chloride, i.e. `Cl^-`, i.e. elemental chlorine has acted as an OXIDANT.

The designated oxidation states, which are of course fictional, thus do reflect Periodic structure, and is conceived to represent the number of electrons the atom takes up (upon reduction) or loses (upon oxidation). The oxidation state method to treat redox reactions is of course a formalism, a convenient fiction that is nertheless sometimes useful to employ.

And thus for perchlorate.....

`"Oxidation:"`
`1/2Cl_2 +4H_2O rarr ClO_4^(-)+8H^(+) + 7e^(-)` `(i)`

`"Reduction:"`
`1/2O_2 +2e^(-) rarr O^(2-)` `(ii)`

I will let you balance it. How do you do that?

The given elements manifestly have different END oxidation states in their compounds. Of course, as the ELEMENT, they are assumed to have an oxidation state of `0`.