JEE Main · 2019 · 10 Apr 2019 · Shift 2 · d and f Block Elements

First ionisation enthalpy broadly rises across the $3d$ series as the nuclear charge builds up, so $\mathrm{Ti}$, with the fewest $d$ electrons, parts with an electron most easily and sits lowest. $\mathrm{Mn}$ comes next, $\mathrm{Ni}$ higher still, and $\mathrm{Zn}$ highest of all because its filled $3d^{10}4s^2$ shell is especially stable and reluctant to ionise. The order is therefore $\mathrm{Ti}<\mathrm{Mn}<\mathrm{Ni}<\mathrm{Zn}$.