An ionic compound is best described as a compound made up of a cation and anion.
Ionic compounds consist of positively charged ions (cations) and negatively charged ions (anions) that are held together by strong electrostatic forces known as ionic bonds. Typically, cations are formed from metals that lose electrons, while anions are formed from nonmetals that gain electrons. This combination results in a neutral compound overall, where the total positive charge equals the total negative charge. The other options provided do not accurately describe ionic compounds:
- b: A compound made up of only nonmetals does not indicate the presence of ions.
- c: A compound made up of hydrogen and either a nonmetal or a polyatomic anion describes acids or molecular compounds, not ionic compounds.
- d: A compound made up of only metals suggests an alloy rather than an ionic compound.
Therefore, option a is the correct choice.