Which of the following chlorides is insoluble in water?

Analyze the question: You're asked which chloride does not dissolve in water. This is a question on the solubility rules for salts.

Concept: Most chlorides are soluble in water. The common exceptions are:

• Silver chloride (AgCl)
• Lead(II) chloride (PbCl₂), which is only soluble in hot water
• Mercury(I) chloride (Hg₂Cl₂)

Solution, option by option:

• A. AgCl is insoluble. It forms a white precipitate. This is the basis of the classic test for chloride ions: add AgNO₃ solution and a white precipitate forms, which dissolves in dilute NH₃(aq).
• B. KCl is soluble, because all salts of Group 1 metals (K⁺, Na⁺) are soluble.
• C. NH₄Cl is soluble, because all ammonium salts are soluble.
• D. ZnCl₂ is soluble. It is a typical metal chloride that dissolves readily in water.

Answer: The only insoluble chloride is AgCl, which is option A.

Tip: Remember the rule "All Na⁺, K⁺, and NH₄⁺ salts are soluble," and for chlorides, remember the exceptions Ag, Pb, Hg. A quick way to recall this is "Silver and lead chlorides stay in the bed (precipitate)."