Which one of the following compounds is insoluble in water?

• A. NaNO_3
• B. NH_4Br
• C. K_2SO_4
• D. AgCl

Answer: (D)

Verified step by step guidance

1. Understand that solubility in water depends on the nature of the compound and common solubility rules in chemistry.
2. Recall that most nitrates (NO_3^-), ammonium salts (NH_4^+), and alkali metal salts (like K^+) are generally soluble in water.
3. Recognize that NaNO_3, NH_4Br, and K_2SO_4 all fall into these categories, so they are expected to be soluble.
4. Know that silver chloride (AgCl) is a classic example of a compound that is insoluble in water due to the low solubility of most silver halides.
5. Therefore, by applying solubility rules, identify AgCl as the compound that is insoluble in water.