Which of the following compounds is insoluble in water at 25 °C?

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

Answer: (B)

Verified step by step guidance

1. Recall the general solubility rules for ionic compounds in water at 25 °C. These rules help predict whether a compound will dissolve (be soluble) or not (be insoluble).
2. Identify the ions in each compound: NH_4Br contains NH_4^+ and Br^-, AgCl contains Ag^+ and Cl^-, NaNO_3 contains Na^+ and NO_3^-, and K_2SO_4 contains K^+ and SO_4^{2-}.
3. Apply the solubility rules: Ammonium (NH_4^+) salts and nitrates (NO_3^-) are generally soluble in water. Most potassium (K^+) salts are also soluble. Bromides (Br^-) are usually soluble except when paired with certain ions, but NH_4Br is soluble.
4. Silver chloride (AgCl) is a well-known exception to solubility rules; most silver salts are insoluble except for a few exceptions. AgCl is commonly insoluble in water at 25 °C.
5. Conclude that among the given compounds, AgCl is insoluble in water at 25 °C, while the others are soluble.