[Borek]

so,in the end the K_sp of salt XY is higher than K_sp for salt X₂Y₃ then i can know that salt XY is more soluble than salt X₂Y₃.

If by "i can know that salt XY is more soluble than salt X₂Y₃" you mean "I will get to the wrong conclusion that salt XY is more soluble than salt X₂Y₃" - you are right.

[killer120]

so,in the end the K_sp of salt XY is higher than K_sp for salt X₂Y₃ then i can know that salt XY is more soluble than salt X₂Y₃.

If by "i can know that salt XY is more soluble than salt X₂Y₃" you mean "I will get to the wrong conclusion that salt XY is more soluble than salt X₂Y₃" - you are right.

maybe my English is too weak.....i can't get what you trying to tell me...about the question you give....am i giving the correct answer?

[killer120]

Rank the following five salts in order of decreasing solubility, in terms of mass per unit volume.
(The most soluble gets rank 1, the least soluble gets rank 5.)

Ag3PO4     (Ksp = 1.80×10-18)
Ag2CrO4     (Ksp = 9.00×10-12)
Ca5(PO4)3F     (Ksp = 1.00×10-60)
Ca3(PO4)2     (Ksp = 1.30×10-32)
AgCl     (Ksp = 1.60×10-10)

So here is my work:

i first found the concentration of the ions:
Ag3PO4 : 1.60685E-5 M
Ag2CrO4 : 1.31037E-4 M
Ca5(PO4)3F : 6.109086E-8 M
Ca3(PO4)2 : 1.644765E-7 M
AgCl : 1.264911E-5 M

Then i used the concentrations and multiplied it by the molar mass and got the following solubilities [g / L]
Ag3PO4 : .0067259 g/L
Ag2CrO4 : .0434687 g/L
Ca5(PO4)3F : 3.0808E-5 g/L
Ca3(PO4)2 : 5.10167E-5 g/L
AgCl : .0081288 g/L

So the salt with the highest solubility would be the salt with the highest number:
3) Ag3PO4
1) Ag2CrO4
5) Ca5(PO4)3F
4) Ca3(PO4)2
2) AgCl

The rank that i have shown is incorrect 
and i dont know why
can someone PLEASE check my work
THANK YOU!!

ya.....i know the answer already...
the calculation of AgCl really has problem with it!
the answer for this question is actually like this:
2) Ag3PO4
1) Ag2CrO4
5) Ca5(PO4)3F
4) Ca3(PO4)2
3) AgCl(0.001813g/L)
am i right?