Question: Is Mg3(PO4)2 ( Magnesium Phosphate ) Soluble or Insoluble in water ?
Answer: Mg3(PO4)2 ( Magnesium Phosphate ) is Insoluble in water

Mg3(PO4)2 ( Magnesium Phosphate ) is Insoluble in water
What is Soluble and Insoluble ?
Solubility
Solubility
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent. The solubility of a substance fundamentally depends on the physical and chemical properties of the solute and solvent as well as on temperature, pressure and the pH of the solution. The extent of the solubility of a substance in a specific solvent is measured as the saturation concentration, where adding more solute does not increase the concentration of the solution and begins to precipitate the excess amount of solute. The solubility of a substance is an entirely different property from the rate of solution, which is how fast it dissolves.
https://en.wikipedia.org/wiki/Solubility

Insoluble
Insoluble

The term insoluble is often applied to poorly or very poorly soluble compounds. A common threshold to describe something as insoluble is less than 0.1 g per 100 mL of solvent.
https://en.wikipedia.org/wiki/Solubility

Soluble List
KClO3 ( Potassium chlorate )
KNO3 ( Potassium nitrate )
K2CO3 ( Potassium carbonate )
LiNO3 ( Lithium nitrate )
MgBr2 ( Magnesium bromide )
NaI ( Sodium iodide )
KC2H3O2 ( potassium acetate )
FeSO4 ( Iron(II) sulfate )
CuSO4 ( Copper sulfate )
Na2S ( sodium sulfide )
Na3PO4 ( Trisodium phosphate )
RbCl ( Rubidium chloride )
BaBr2 ( Barium bromide )
AlCl3 ( Aluminium chloride )
HNO3 ( Nitric acid )
FeCl2 ( Iron dichloride )
BaI2 ( Barium iodide )
MnCl2 ( Manganous chloride )
AgClO3 ( Silver chlorate )
CoBr2 ( Cobalt bromide )
K2S ( Potassium sulfide )
CuCl2 ( Copper chloride )
K3PO4 ( Potassium phosphate )
KI ( Potassium iodide ) 
(NH4)2SO4 ( AMMONIUM SULFATE )
Na2CO3 ( Sodium carbonate )
CaBr2 ( Calcium bromide )
Li3PO4 
NH4NO3 ( Ammonium nitrate )
HgCl2 ( Mercury(II) chloride )
BaCl2 ( Barium chloride )
NaSO4 ( Sodium sulfate )
HCl ( Hydrochloric acid )
AgC2H3O2 ( Silver acetate )
pb(c2h3o2)2 ( Lead(II) acetate )
KSO4
Li2CO3 ( Lithium carbonate )
Li2S ( Lithium sulfide )
Hg2SO4 ( MERCUROUS SULFATE )
Pb(NO3)2 ( Lead dinitrate )
NH4Cl ( AMMONIUM CHLORIDE )
NH4OH ( ammonium hydroxide )
ZnSO4 ( Zinc sulfate )
CaCrO4 ( CALCIUM CHROMATE )
CsOH ( Cesium hydroxide )
(NH4)3PO4 ( Ammonium phosphate )
LiOH ( Lithium hydroxide )
BaS ( Barium sulfide )
K2SO4 ( POTASSIUM SULFATE )
Na2SO4 ( Sodium sulfate )
NiCl2 ( NICKEL CHLORIDE )
NiBr2 ( NICKEL BROMIDE )
MgSO4 ( magnesium sulfate )
NH4I ( Ammonium iodide )
HgCl2 ( MERCURIC CHLORIDE )
MgCl2 ( Magnesium chloride )
H2SO4 ( Sulfuric acid )
CaCl2 ( Calcium chloride )
BaF2 ( Barium fluoride )
Na3PO4 ( sodium phosphate )
Cu(NO3)2 ( Copper(II) nitrate )
AgNO3 ( Silver nitrate ) 
MgC2O4 ( Magnesium oxalate )
KCl ( Potassium chloride )
Al2(SO4)3 ( Aluminium sulfate )
Ca(NO3)2 ( Calcium nitrate )
MgS ( Magnesium sulfide )
NaNO3 ( Sodium nitrate )
NiI2 ( Nickel(II) iodide )
(NH4)2CO3 ( AMMONIUM CARBONATE )
HCN ( hydrogen cyanide )
NaBr ( sodium bromide )
NH4Br ( AMMONIUM BROMIDE )
AlCl3 ( aluminum chloride  )
SrS ( Strontium sulfide ) 
FeCl3 ( Iron(III) chloride )
LiBr ( Lithium bromide )
KOH ( Potassium hydroxide )
ZnBr2 ( Zinc bromide )
NH3 ( ammonia )
NaOH ( Sodium hydroxide )
CuBr2 ( Copper(II) bromide )
Fe(NO3)2 ( Iron(II) Nitrate )
nahco3 ( Sodium bicarbonate )
CaSO4 ( calcium sulfate )
NaCl ( sodium chloride )
KBr ( Potassium bromide )
(NH4)2S ( Ammonium sulfide ) 
LiCl ( Lithium chloride )
ZnCl2 ( Zinc chloride )
Ba(OH)2 ( Barium hydroxide )
CoCl2 ( Cobalt(II) chloride )
Ba(NO3)2 ( Barium nitrate )
AgClO4 ( Silver perchlorate )
Mg(NO3)2 ( MAGNESIUM NITRATE )
Zn(NO3)2 ( Zinc nitrate )
Sr(OH)2 ( Strontium hydroxide )
Fe(NO3)3 ( Iron(III) nitrate )
NaC2H3O2 ( sodium acetate )
Ba(ClO4)2 ( BARIUM PERCHLORATE )
HgSO4 ( Mercury(II) sulfate )
Ca(C2H3O2)2
C4H6O4Ba ( Barium Acetate )
K2O ( Potassium oxide )
NaClO ( sodium hypochlorite )
CuCl ( Copper(I) chloride )
Sr(NO3)2 ( Strontium nitrate )
Cu(C2H3O2)2 
kclo4 ( POTASSIUM PERCHLORATE )
NaClO4 ( Sodium perchlorate )
NaClO3 ( SODIUM CHLORATE )
C4H6O4Ca ( Calcium Acetate )
Zn(CH3COO)2 ( Zinc acetate )
CH3OH ( methanol )
Ba(C2H3O2)2
Al(NO3)3 ( aluminum nitrate )
K2SO3 ( Potassium sulfite )
H3PO4 ( Phosphoric acid )
MnI2 ( Manganese(II) iodide )
CoSO4
CsCl
Ca(ClO4)2
MgI2 ( magnesium iodide )
Ni(NO3)2 ( Nickel(II) nitrate )
Cu(CH3COO)2 ( Copper(II) Acetate )
C12H22O11 ( sucrose )
Cr(NO3)2 
NiSO4 ( Nickel(II) sulfate )
aluminum acetate
NH4C2H3O2
NaPO4
Iron(III) Acetate
H2SO3 ( Sulfurous acid )
Co(NO3)2 ( Cobalt(II) nitrate )
Mn(NO3)2 ( Manganese(II) Nitrate )
Li2SO4 ( Lithium sulfate )
SO2 ( Sulfur dioxide )
AlBr3 ( ALUMINUM BROMIDE )
C2H7NO2 ( Ammonium Acetate )
Na2SO3 ( Sodium sulfite )
ZnI2 ( Zinc iodide )
HClO4 ( Perchloric acid )
HBr ( Hydrogen bromide )
CaI2 ( Calcium iodide )

Insoluble List
Ag2CO3 ( Silver carbonate )
Hg2I2 ( Mercury(I) iodide )
CuCO3 ( Copper carbonate )
BaCO3 ( Barium carbonate )
AgOH ( Silver Hydroxide )
Fe2S3 ( Iron(III) sulfide )
MgCO3 ( Magnesium carbonate )
Ag2O ( Silver oxide )
CuS ( Copper(II) sulfide )
Hg2Cl2 ( Mercury(I) chloride )
AgCO3 ( Silver carbonate )
PbCl2 ( Lead dichloride )
PbI2 ( Lead(II) iodide )
Cu(OH)2 ( Copper(II) hydroxide )
AgCl2 ( Silver chloride )
AgCl ( Silver chloride )
Ag3PO4 ( Silver phosphate )
Cu3(PO4)2 ( Copper(II) phosphate )
FePO4 ( Iron(III) phosphate )
NiCO3 ( Nickel(II) carbonate )
SrCO3 ( Strontium carbonate )
Ag2S ( Silver sulfide )
AlPO4 ( Aluminum phosphate )
cui2 ( copper iodide )
pbcro4 ( LEAD CHROMATE )
PbF2 ( Lead fluoride )
Fe(OH)3 ( Ferric hydroxide )
Fe2O3 ( Iron(III) oxide )
PbS ( Lead(II) sulfide )
PbSO4 ( Lead(II) sulfate )
Ca3(PO4)2 ( calcium phosphate )
BaSO4 ( Barium sulfate )
hno2 ( Nitrous acid )
agl
Ba3(PO4)2 ( barium phosphate )
PbI ( Lead(II) iodide )
HgI2 ( Mercury diiodide )
Hg2Br2 ( Mercury(I) bromide )
Al2S3 ( Aluminium sulfide )
Ag2CrO4 ( Silver chromate )
Pb(OH)2 ( Lead(II) hydroxide )
Cu(OH)2 ( Copper(II) hydroxide )
Li3PO4 ( Lithium Phosphate )
SrSO4 ( Strontium sulfate )
AgBr ( silver bromide )
MgO ( MAGNESIUM OXIDE )
Zn(OH)2 ( zinc hydroxide )
PbBr2 ( Lead(II) Bromide )
ZnCO3 ( ZINC CARBONATE )
Zn3(PO4)2 ( Zinc Phosphate )
Mg(C2H3O2)2
FeS ( Iron(II) sulfide )
CaCO3 ( Calcium carbonate )
Mg(OH)2 ( Magnesium hydroxide )
Mg3(PO4)2 ( Magnesium Phosphate )
AgI ( Silver iodide )
FeCO3 ( Iron(II) carbonate )
Ag2SO4 ( Silver sulfate )
ZnS ( Zinc sulfide )
Al(OH)3 ( Aluminium hydroxide )
PbCO3 ( Lead carbonate )
AgSO4 ( silver(II) sulfate )
Fe(OH)2 ( Iron(II) hydroxide )
NiS ( Nickel sulfide )
CdCO3 ( CADMIUM CARBONATE )
Mn(OH)2 ( Manganese hydroxide )
CoCO3 ( Cobalt(II) carbonate )
Ni(OH)2 ( Nickel(II) hydroxide )
BaCrO4 ( Barium chromate )
CoS ( cobalt(ii) sulfide )
Co(OH)2 ( Cobalt(II) hydroxide )
FeO(OH) ( Iron(III) hydroxide )
CuCrO4 ( Copper(II) chromate )
Cd(OH)2 ( Cadmium hydroxide )
CaF2 ( Calcium fluoride )
Cr2S3 
Pb3(PO4)2
CaC2O4
MnCO3 ( Manganese(II) carbonate )
HC2H3O2

low solubility ( Slightly soluble )
Ca(OH)2 ( Calcium hydroxide )
CaS ( Calcium sulfide )
PbCl2 ( Lead dichloride )
H2CO3 ( Carbonic acid )
H2S ( Hydrogen sulfide )

We get answers from
Resources
www.quora.com
answers.yahoo.com
answers.com
www.quia.com
quizlet.com
www.reference.com
socratic.org
https://en.wikipedia.org
http://periodic-table-of-elements.org/SOLUBILITY
pubchem.ncbi.nlm.nih.gov
https://en.wikipedia.org/wiki/Solubility

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Question: Is Mg3(PO4)2 ( Magnesium Phosphate ) Soluble or Insoluble in water ?
Answer: Mg3(PO4)2 ( Magnesium Phosphate ) is Insoluble in water