Final answer:
A substance that conducts electricity well in both solid and liquid forms is most likely to exhibit metallic bonding, as this allows for free electrons to move and conduct electricity.
Step-by-step explanation:
If a pure substance is known to be a good conductor of electricity in both its solid and liquid phases, the type of bonding in the substance is metallic or ionic. Metallic bonding characterizes metals, where valence electrons are free to move throughout the structure, allowing electrical conductivity in solid and often in molten states. Ionic bonding is where the substance is composed of positive and negative ions held together by strong electrostatic forces. In solid form, ionic compounds do not conduct electricity because the ions are fixed in place but conduct when melted due to free movement of ions. Considering the question, metallic bonding is the correct answer because ionic compounds typically do not conduct electricity in solid form.