Explain the following observations giving an appropriate reason for each:
(i) The enthalpies of atomization of transition elements are quite high.
(ii) There occurs much more frequent metal-metal bonding in compounds of heavy transition metals (i.e., 3rd series).
(iii) Mn²⁺ is much more resistant than Fe²⁺ towards oxidation.

I) Transition metals have high effective nuclear charge and more number of valence electrons. Therefore, they form strong metallic bonds; as a result, the enthalpy of atomization is very high.
II) The presence of valence electrons and unpaired d-orbital electrons helps heavy transition metals to form metallic bonds.
III) Due to the stability of Mn²⁺ because it has a half-filled (3d⁵) d-orbital, it does not oxidize easily. But Fe²⁺ has a 3d⁶ configuration and it can lose one electron to get a stable d⁵ configuration. Therefore, it can be easily oxidized.