Which pair of elements from the same group shows the smallest difference in first ionization enthalpy?
In group 13, Ga and In have a smaller ionization enthalpy difference due to d-block contraction effects, unlike B-Al, where the drop is larger due to a new shell.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Periodic Trends - Atomic Radii Ionic Radii and Ionization Enthalpy