Explain the following observations :
(i) Copper atom has completely field d orbitals `(3d^(10))` in its ground state, it is regarded as a transition element.
(ii) `Cr^(2+)` is a stronger reducing agent than `Fe^(2+)` in aqueous solutions.

Explanation

The outer configuratin of copper is `3d^(10)4s^(1).` In addition to + 1, it shows an oxidation state of +2. In +2 state, the configuration is `d^(9)` .i.e., the sub shell is incompletely filled. Hence, it is a transition element.
(iii), `Cr^(2+)` strong reducing agent than `Fe^(2+)` because `Cr^(2+)` get oxidised to `Cr^(3+)` easily which has half filled `t_(2)^(3)g` configuration which is more stable is more stable than `3d^(5)` in `Fe^(3+).`