Why does the ionisation enthalpy of V is less than Ti ?

In transition metals the electrons are removed from 4s sub shell first (to determine ionization enthalpy). When we consider filling of electrons, first 4s is filled then the 3d and this gradually increase the shielding of 4s electrons from the nucleus.

The outer electronic configuration of titanium is 3d24s2. There are only 2 electrons in ‘3d’ shell which are shielding the 4s electrons.

The outer electronic configuration of Vanadium is 3d34s2. There are 3 electrons in ‘3d’ shell which are shielding the 4s electrons from the nucleus which means 4s electrons are easy to remove.

Hence ionisation enthalpy of Vanadium is less than Titanium.