Question

which property best indicates that a compound contains an ionic bond?
it is insoluble in water.
it can be easily flattened.
it has a low boiling point.
it conducts electricity when molten.

Explanation:

Ionic compounds consist of ions. When molten, the ions are free to move and can conduct electricity. Ionic compounds are generally soluble in water (so the first option is wrong). They are brittle (not easily flattened, so the second option is wrong). They have high boiling points (so the third option is wrong).

Answer:

It conducts electricity when molten.