The first ionization enthalpies of the elements of the first transition series (Ti → Cu)

increase as the atomic number increases

The correct answer is (1) increase as the atomic number increases, then the first ionization enthalpies of the elements in the first transition series (Ti to Cu) indeed increase as the atomic number increases.

The first ionization enthalpy refers to the energy required to remove the first electron from an atom in its gaseous state. In the first transition series, as we move from titanium (Ti) to copper (Cu) across the period, the atomic number increases, and so does the number of protons in the nucleus.

The increase in the number of protons leads to a stronger effective nuclear charge, which attracts the electrons more strongly. Consequently, it becomes increasingly difficult to remove an electron from the atoms, requiring higher energy. Therefore, the first ionization enthalpies of the elements in the first transition series generally increase as the atomic number increases.