What is the charge of phosphate in K3PO4?

The correct answer is (- 3).
Elements in the periodic table are arranged according to the number of ions they have, for example, sodium a group 1 element has +1 cation, group 2 elements like calcium has +2 cation. Potassium is a group 1 element which means it has one cation. However, some elements from numerous different ions.

Example of such is phosphorus, it can exist as -3 or -4. Since we have 3 potassium which forms a total of 3 positive charges. Depending on the positive charge of the element attached to it (k3) phosphorus must have the (-3) charge to counter the (+3) charge to get the resultant. This means, in this reaction phosphorus is - 3.

Different atoms interact with one another on an atomic level and produce a resultant charge. Certain non-metal ions are especially skilled at having more than one oxidation state and charge on their atom. For instance, phosphate can have a charge of -3 or -4. Depending on the positive cations attached to it, one can easily determine its charge.

In this case it has 3 potassium attached to it. As potassium has a charge of +1, it means that the total positive charge resulting from potassium ions is +3. Hence, the total charge needed to counteract these cations is -3 which should be the total charge in the phosphate ion.