Final answer:
The pairing of Ca2+ and O2- ions would form the ionic substance with the highest lattice energy due to the greater product of their charges compared to the other options presented.
Step-by-step explanation:
The ionic substance with the highest lattice energy out of the given options would be Ca2+ and O2- (option 3). Lattice energy is highly dependent on the charges of the ions involved; the greater the charges, the higher the lattice energy. Given this relationship, a combination of a divalent cation and a divalent anion, such as Ca2+ and O2-, would result in the highest lattice energy because the product of their charges (2 x 2 = 4) is greater than the product of the charges for any of the other ion pairs listed (1 x 1 = 1 for Na+ and Cl-, K+ and Br-, and Mg2+ and F-). Furthermore, a comparison of the calculated lattice energies supports this: MgO, which is similar to CaO in terms of charges, has a lattice energy of 3795 kJ/mol, which is significantly greater than that of NaF, which has a lattice energy of 910 kJ/mol. Thus, by extrapolation, CaO would have a higher lattice energy than a compound composed of ions with a +1 and -1 charge, such as Na+ and Cl- (NaCl).