Which of the following substances is soluble in water?

• A. BaSO_4
• B. PbI_2
• C. AgCl
• D. NaNO_3

Answer: (D)

Verified step by step guidance

1. Recall the general solubility rules for ionic compounds in water, which help predict whether a substance will dissolve.
2. Note that most nitrates (NO_3^-) are soluble in water without exception, so NaNO_3 is expected to be soluble.
3. Check the solubility of sulfates (SO_4^{2-}): while many sulfates are soluble, BaSO_4 is an exception and is generally insoluble.
4. Consider halides (like I^- and Cl^-): many are soluble, but PbI_2 and AgCl are known to be poorly soluble or insoluble in water.
5. Conclude that among the given substances, NaNO_3 is soluble in water due to the nitrate ion's high solubility, while BaSO_4, PbI_2, and AgCl are not.