According to solubility rules, which statement best explains why silver chromate (Ag2CrO4) is sparingly soluble in water?

• A. Silver chromate is soluble because all chromate salts are soluble.
• B. All silver salts are highly soluble in water.
• C. Chromate ions always form soluble compounds with transition metals.
• D. Most chromate salts are insoluble except those of alkali metals and ammonium.

Answer: (D)

Verified step by step guidance

1. Recall the general solubility rules for chromate salts: most chromate (CrO4^{2-}) salts are insoluble in water except those containing alkali metal ions (like Na^+, K^+) and ammonium (NH4^+).
2. Consider the nature of silver (Ag^+) ions: many silver salts, such as AgNO3, are soluble, but silver halides and some other silver salts tend to be insoluble or sparingly soluble.
3. Combine these two points to analyze silver chromate (Ag2CrO4): since chromate salts are generally insoluble except with alkali metals and ammonium, and silver is not an alkali metal or ammonium, silver chromate is expected to be sparingly soluble.
4. Understand that the low solubility of silver chromate arises from the insolubility of chromate salts with transition metals like silver, which leads to the formation of a solid precipitate rather than dissolving fully in water.
5. Therefore, the best explanation is that most chromate salts are insoluble except those of alkali metals and ammonium, which explains why silver chromate is sparingly soluble.