Which One of the Following Substances Is Most Likely Composed

Multiple Choice

Which one of the following substances is most likely composed of ions rather than distinct formula units, when it is in the solid state?

A) Al₂O₃, m.p. 2000°C, hard substance
B) CrO₃, m.p. 196°C, soft substance
C) Mn₂O₇, m.p. 5.9°C, soft in solid state
D) OsO₄, m.p. 40°C, soft substance
E) SeO₃, m.p. 118°C, relatively soft