Reactivity of transition elements decreases almost regularly from $Sc$ to $Cu$. Explain.

(N/A) The reactivity of transition elements is primarily determined by their ability to lose electrons,which is related to their ionization enthalpy.
As we move from $Sc$ $(Z=21)$ to $Cu$ $(Z=29)$ in the $3d$ series,the effective nuclear charge increases due to poor shielding by $d$-electrons.
This leads to an increase in the first and second ionization enthalpies.
Consequently,the tendency to lose electrons decreases,making the elements less reactive.
Additionally,the increase in the enthalpy of atomization (due to stronger metallic bonding as the number of unpaired electrons increases up to $Cr$) also contributes to the decrease in reactivity.