What characterizes an ionic compound?

An ionic compound is characterized by the presence of positive and negative ions that are held together by strong electrostatic forces known as ionic bonds. These compounds typically form when one atom, usually a metal, donates one or more electrons to another atom, usually a nonmetal, leading to the creation of positively charged cations and negatively charged anions. This ionic nature results in distinct properties such as high melting and boiling points, and the ability to conduct electricity when dissolved in water or melted.

The other options describe different bonding scenarios or states of matter that do not pertain to the fundamental characteristics of ionic compounds. For instance, equal sharing of electrons describes covalent bonding rather than ionic bonding. Similarly, molecules with polar covalent bonds do not achieve the complete transfer of electrons needed to form ionic bonds. Additionally, while many ionic compounds are solid at room temperature, they are not exclusively liquid, as some may be gaseous or liquid under specific conditions. Therefore, the defining feature of ionic compounds is indeed the presence of positive and negative ions.