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

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

Answer: (A)

Verified step by step guidance

1. Recall the general solubility rules for ionic compounds in water, which help predict whether a compound will dissolve or remain insoluble.
2. Identify that compounds containing alkali metal ions (like K\textsuperscript{+}) and the ammonium ion (NH\textsubscript{4}\textsuperscript{+}) are generally soluble in water.
3. Recognize that most nitrate (NO\textsubscript{3}\textsuperscript{−}) salts are soluble without exception.
4. Note that sulfate salts (SO\textsubscript{4}\textsuperscript{2−}) are usually soluble, with some exceptions like barium sulfate or lead sulfate, but potassium sulfate (K\textsubscript{2}SO\textsubscript{4}) is soluble.
5. Understand that silver chloride (AgCl) is a classic example of an insoluble salt because silver halides (except AgF) are generally insoluble in water.