Question

Which is not a quality of an ionic compund, brittleness, hardness, molten compound conducts electricity.

Answer 1

Well, it wouldn't make sense for them to be both brittle and hard, so that narrows it down to those two.

We also know that when it's molten, it will conduct electricity well.

Anyway, the answer is "hardness."

Ionic compounds are brittle because they form a sort of crystalline-esque structure when they bond. Thus, when you try to bend this structure, it will slide out of place, breaking the crystalline structure.