Final answer:
b. high boiling point .The least characteristic property of ionic compounds is being a poor electrical conductor when molten, since molten ionic compounds generally conduct electricity well due to the mobility of their ions.
Step-by-step explanation:
You asked which of the following properties is least characteristic of typical ionic compounds: high melting point, high boiling point, brittleness, poor electrical conductor when solid, or poor electrical conductor when molten.
Ionic compounds are known for having high melting points and boiling points due to the strong electrostatic forces between the ions. They are also brittle and can break along planes when under stress.
However, they are poor electrical conductors in the solid state because the ions are locked in a rigid lattice structure and cannot move freely. When molten, ionic compounds can conduct electricity because the ions are free to move.
Therefore, the option "e. poor electrical conductor when molten" is the least characteristic of ionic compounds, since they typically conduct electricity well when melted.