Number of Ions in KCl : Potassium chloride

To determine the number of ions in KCl  you need to recognize the Potassium ion (K+) and the Chloride ion (Cl -).  

For the ionic charges on elements, see  Finding the Ionic Charge for Elements... .

You can either memorize the polyatomic ions or, if you are allowed, you can look it up on a table of polyatomic ions (Memorizing and Using the List of Poly...).
For Potassium chloride there is one K+  ion and one Cl- ion.  So there are a total of two ions for one formula unit of KCl .

If you were given one mole of KCl   you would have1 mole of K+ ions and 2 moles of Cl - ions.