Question

The ionization enthalpy (first and second) in the first series of the transition elements varies irregularly.
If true enter $1$ else $0$.

Answer 1

In the first transition series, the first and second ionization enthalpy values increases slowly from left to right with certain irregularities.
As the nuclear charge increases, the attraction between the nucleus and outer electron increases due to which the ionization enthalpy increases.

However the electron is added to (n-1) d subshell, the screening effect increases. Thus the increase in the nuclear charge is opposed by the increase in the screening effect. Hence, the ionization enthalpy values slowly increases.

The removal of electron alters the energies of 4s and 3d orbitals which results in reorganization energy accompanying ionization with some gains in exchange energy with increase in the number of electrons in the $d^n$ configuration and from transference of s electrons into d orbitals. This results in irregularities in the ionization enthalpy values.

Chromium has lower first ionization enthalpy value as the loss of one electron gives stable $\left(3d^5\right)$ configuration. Zinc has high ionization enthalpy as electron is to be removed from 4s orbital of stable $\left(3d^{10}4s^2\right)$ configuration.