The Ksp expression for Ba3(PO4)2 is written as follows
first: write the equation for dissociation of Ba3(PO4)2
that is Ba3(PO4)2(s) ----> 3Ba ^2+(aq) + 2 Po4 ^3-(aq)
solubility product (KSP) is therefore= (Ba^2+)^3(Po4^3-) ^2
it is the concentration of each ion raised to the power of their coefficient in the formula