Account for the following:

(i) Mn²⁺ is more stable than Fe²⁺ towards oxidation to +3 state.

(ii) The enthalpy of atomization is lowest for Zn in 3d series of the transition elements.

(iii) Actinoid elements show a wide range of oxidation states.

i) Electronic configuration of Mn²⁺ is [Ar]¹⁸3d⁵
   Electronic configuration of Fe²⁺ is [Ar]¹⁸ 3d⁶

It is known that half-filled and fully-filled orbitals are more stable. Therefore, Mn in +2 state has a stable d⁵ configuration. Therefore, Mn²⁺ shows resistance to oxidation to Mn³⁺. Also,

e²⁺ has 3d⁶ configuration and by losing one electron, its configuration changes to a more stable 3d⁵ configuration.

Therefore, Fe²⁺ gets oxidised to Fe³⁺ easily.

ii) The extent of metallic bonding an element undergoes, decides the enthalpy of atomisation.

The more extensive the metallic bonding of an element, the more will be its enthalpy of atomisation. In all transition metals (except Zn, electronic configuration:  3d¹⁰ 4s²), there are some unpaired electrons that account for their stronger metallic bonding. Due to the absence of these unpaired electrons, the inter-atomic electronic bonding is the weakest in Zn and as a result, it has the least enthalpy of atomisation.

iii) Actinides exhibit larger oxidation states because of very small energy gap between 5f, 6d and 7s sub-shells. The energies are calculated on the basis of (n+l) rule. The (n+l) values of the three orbitals are:

5 f = 5 + 3 = 8
6 d = 6 + 2 = 8
7 s = 7 + 0 = 7

Since, all the values are almost same, therefore all orbitals can involve in bonding resulting in larger oxidation number for actinoids.