How do you find the number of ions in a given salt?
Your question is unclear.
There are atoms in ions. Sometimes there is only the 1 atom in an ion. In such an ion the atom would have a positive or negative charge (i.e. a deficiency or excess of electrons):
You have to know the formulas for all the ions.
An ionic compound contains both positive and negative ions.
The only polyatomic ion is
You must be able to write the formulas corresponding to the names of these ions.
The total charges on the cations must equal the total charges on the anions.