Based on the solubility rules, which of the following compounds is most likely to be insoluble in water?

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

Answer: (D)

Verified step by step guidance

1. Review the common solubility rules for ionic compounds in water, focusing on the solubility of ammonium (NH_4^+), alkali metal ions (such as Na^+ and K^+), and common anions like bromide (Br^-), nitrate (NO_3^-), and sulfate (SO_4^{2-}).
2. Recall that compounds containing ammonium (NH_4^+) and alkali metal ions (Na^+, K^+) are generally soluble in water regardless of the anion they are paired with.
3. Note that bromides (Br^-), nitrates (NO_3^-), and sulfates (SO_4^{2-}) are typically soluble, with some exceptions mainly for sulfates with heavy metals, but not for alkali metals or ammonium.
4. Understand that silver chloride (AgCl) is a classic example of an insoluble salt because silver (Ag^+) halides (except AgF) are generally insoluble in water according to solubility rules.
5. Conclude that among the given compounds, NH_4Br, NaNO_3, and K_2SO_4 are all soluble, while AgCl is the one most likely to be insoluble in water.