A phosphate ion has a 3- charge and a potassium ion has a 1+ charge.
In order to form a neutral compound, 3 potassium ions are needed to satisfy the 3- charge on the phosphate ion.
Three potassium ions (
An ionic compound is composed of positive and negative ions such that the overall charge is zero. If the positive and negative ions do not have the same magnitude of charge, then they will need to combine in a ratio which will produce an equal positive and negative charge.
In the case of the potassium and phosphate ions, potassium ions have a charge of