Lowest enthalpy  atomisation among the following is of:

In general, d-block elements exhibit higher enthalpies of atomization due to stronger covalent bonds between atoms, which result from unpaired (n-1) d electron participation in covalent bonding in addition to ns electron participation in metallic bonding. In the 3d-series from$\mathrm{Sc}$ (Z = 21) to Zn (Z = 30), zinc has the lowest enthalpy of atomization (126 kJ mol1) because it lacks an unpaired (n-1) d electron that may be used for extra covalent bonding.

As number of unpaired ${\mathrm{e}}^{-}\uparrow ,{\mathrm{\Delta }}_{\text{atomisation }}\mathrm{H}\uparrow$.