Which of the following compounds is most soluble in water?

• A. AgCl
• B. PbBr_2
• C. NaNO_3
• D. BaSO_4

Answer: (C)

Verified step by step guidance

1. Step 1: Understand that solubility in water depends largely on the compound's ability to dissociate into ions and the lattice energy of the solid versus the hydration energy of the ions.
2. Step 2: Recognize that ionic compounds containing alkali metal ions (like Na⁺) and nitrate ions (NO₃⁻) are generally very soluble in water due to strong ion-dipole interactions with water molecules.
3. Step 3: Compare the given compounds: AgCl, PbBr₂, BaSO₄ are all salts with ions that tend to form less soluble compounds because of higher lattice energies and lower hydration energies relative to NaNO₃.
4. Step 4: Recall the solubility rules: nitrates (NO₃⁻) are typically soluble with no common exceptions, while chlorides, bromides, and sulfates have varying solubilities and often form precipitates with certain cations.
5. Step 5: Conclude that NaNO₃ is the most soluble compound among the options because it fully dissociates in water and does not form a precipitate, unlike the other salts listed.