(i) Name the element of 3d-transition series which shows maximum number of oxidation states. Why does it show so?
(ii) Which transition metal of 3d-series has positive `E^0(M^(2+)//M)` value and why?
(iii) Out of `Cr^(3+)` and `Mn^(3+)` which is a stronger oxidizing agent and hy? 
(iv) Name a member of the lanthanoid series which is well known to exhibit + 2 oxidation state.
(v) Complete the following equaton: `MnO_(4)^(-) + 8H^(+) + 5e^(-) to`

Explanation

(i) Mn, because of presence of 5 unpaired electrons in 3d-subshell
(ii) Cu, because enthalpy of atomization and ionisation enthalpy is not compensated by enthalpy.
(iii) Mnt because `Mn^(2+)` is more stable due to its half filled (3d) configuration.
(iv) `Eu^(2+) (Eu)`
(v) `MnO_(4)^(-) + 8H^(+) + 5e^(-) + Mn^(2+) + 4H_2O`.