Which ion among the following isoelectronic species with 36 electrons has the highest lattice energy when paired with F⁻
For isoelectronic species (36 electrons), lattice energy increases with charge. Sc³⁺ (Z=21, +3) forms ScF₃ with the highest lattice energy compared to K+, Ca²⁺, or Br⁻.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Genesis of Periodic Classification - Dobereiner Newlands Mendeleev