The equilibrium interatomic spacings of the Na halides and their melting points are listed below. Explain the trend observed. NaF NaCl NaBr Nal Spacing, nm Melting point, C 0.23 0.28 0.29 0.32 988 801 740 660 (b) Explain the melting point trends observed for the alkali metal chlorides as one goes from HCI (-115.8C) to CsCl. (c) Which of these pairs of compounds would you expect to have the higher melting points; CaF2 versus ZrO2; UO, versus CeO2; CaF2 versus Cal2? Explain.