CaO has a substantially larger lattice energy than KF. Which statement best accounts for this difference?
a) The K+ ion is smaller than the Ca2+ ion, leading to stronger attractions and therefore a higher lattice energy in KF.
b) KF has a more closely packed crystal structure than CaO, which reduces the distance between ions and gives KF the greater lattice energy.
c) Both ions in CaO carry charges of ±2, whereas the ions in KF carry charges of only ±1.
d) The greater electronegativity difference between K and F makes the bonds in KF more ionic, so its lattice energy is larger than that of CaO.