Following ions are given :
`Cr^(2+), Cu^(2+), Cu^(+), Fe^(2+),Fe^(3+),Mn^(3+)`
Identify the ion which is
(i) a strong reducing agent.
(ii) unstable in aqueous solution.
(iii) a strong oxidising agent.
Give suitable reason in each.

Explanation

(i) `Cr^(2+)` is a strong reducing agent because `E_(Cr^(3+)//Cr^(2+)=-0.41 V.)^(o)`
The values with other metal ions are positive.
(ii) `Cu^(+)` ion is unstable in aqueous solution because the enthalpy of hydration `Cu^(+)` ion is very small.
(iii) `Cu^(2+)` is a strong oxidising agent because it has a tendency to get reduced with `E^(o)` value of `+0.34` V.