(i) Which transition element in 3d series has positive `E_(M^(2+//)M)^(@)` value and why ?
(ii) Name a member of lanthanoid series which is well known to exhibit to exhibit +4 oxidation state and why?
(b) Account for the following :
(i) The highest oxidation state is exhibited in oxoanions of transition metals.
(ii) HCl is not used to acidify `KMnO_(4)` solution.
(iii) Transition metals have high enthalpy of atomisation.

Explanation

### Step-by-Step Solution:

#### (i) Which transition element in the 3d series has a positive \( E_{M^{2+}/M}^\circ \) value and why?

The transition element in the 3d series that has a positive value of standard reduction potential \( E_{M^{2+}/M}^\circ \) is **Copper (Cu)**.

**Reason:**
1. **Hydration Energy:** Copper has a relatively low hydration energy compared to other transition metals. This means that when Cu is ionized to form \( Cu^{2+} \), the energy released during hydration is not sufficient to compensate for the energy required to remove the electron, resulting in a positive reduction potential.
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