This is a metal oxide, the constituent ions are thus:
The (II) is a naming convention mainly for transition metals, because they may have very many possible cation electron configurations. For instance, (II) means a 2+ charge, (IV) would mean 4+.
Zinc(II) oxide is a compound composed of zinc and oxygen, so what is its formula..?
First of all, the parentheses that follow the transition metal in ionic compounds like this one indicate the oxidation state (or oxidation number) of the metal. This is essentially for these purposes the same thing as its ionic charge (although not exactly!)
This formula indicates that zinc has an oxidation state (ionic charge) of
An important fact worth knowing is that oxygen almost always has an oxidation state of
Remember that formulas for ionic compounds contain the lowest whole number ratio of atoms in the compound, and one of each zinc and oxygen suits this perfectly, so the formula is
All in all, know that the sum of oxidation states in a neuatral compound is always zero, and that you determine the formula based on the oxidation states (ionic charges).
Sorry if this seemed confusing!