An ionic compound is written as AB. Which of the following set is correct about this compound?

Ionic compounds are neutral compounds made up of positively charged ions called cations and negatively charged ions called anions. 

First, the name of the cation is written first followed by the name of the anion. Because most metals form cations and most nonmetals form anions, formulas typically list the metal first and then the nonmetal.

Hence, A=cation (metal), B=Anion(Non-metal)