Salts of Alkali Metals are soluble

e.g. If M = Li, Na, or K, then MX, MX₂, MX₃, etc. are soluble regardless of what X is

Ammonium salts (NH₄⁺) are soluble

e.g. NH₄X, (NH₄)₂X, (NH₄)₃X, etc. are soluble regardless of what X is

Nitrates (NO₃) are soluble

e.g. MNO₃, M(NO₃)₂, M(NO₃)₃, etc. are soluble regardless of what M is

Halides (Cl-, Br-, I-) are soluble

Exceptions: Ag⁺, Hg⁺, Hg²⁺, Cu⁺, Pb²⁺

e.g. If X = Cl, Br or I, then MX, MX₂, MX₃, etc. are soluble unless M = Pb, Hg or Ag

Sulfates (SO₄) are soluble

Exceptions: Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺, Hg²⁺, Ag⁺

e.g. M₂SO₄, MSO₄, M₂(SO₄)₃, etc. are soluble unless M is from group 2 or M = Pb, Hg, or Ag

Carbonates (CO₃), Phosphates (PO₄), and Sulfides (S) are insoluble except for:

(i) The carbonates/phosphates/sulfides of alkalis (because of Rule 1)

(ii) Ammonium carbonate/phosphate/sulfide (because of Rule 2)

Hydroxides (OH) are insoluble or slightly soluble except for the hydroxides of the alkalis (because of Rule 1)

Note: The hydroxides of group 2 (the alkaline earth metals) are slightly soluble. Virtually all other hydroxides are insoluble. Also, ammonium hydroxide is slightly soluble.