The compound that should not dissolve in water (i.e., is insoluble) according to standard solubility rules is typically something like barium sulfate, BaSO₄ , or silver chloride, AgCl. These are classic “insoluble in water” examples used in most solubility rules charts.

Quick Scoop: Core Idea

According to common solubility rules used in high school and intro college chemistry:

  • Most alkali metal (Group 1) salts and ammonium (NH₄⁺) salts are soluble.
  • Most nitrates (NO₃⁻) and acetates (CH₃COO⁻) are soluble.
  • Many chlorides, bromides, and iodides are soluble, except those of Ag⁺, Pb²⁺, and Hg₂²⁺ , which are insoluble (e.g., AgCl).
  • Most sulfates (SO₄²⁻) are soluble, but BaSO₄, PbSO₄, and CaSO₄ are commonly listed as insoluble or only very slightly soluble (BaSO₄ is the go‑to “insoluble” example).
  • Most carbonates (CO₃²⁻), phosphates (PO₄³⁻), and hydroxides (OH⁻) are insoluble unless paired with Group 1 cations or ammonium.

So in a multiple‑choice question that asks:

“According to solubility rules, which compound should not dissolve in water?”

the best answer is usually something like BaSO₄(s) or AgCl(s) , because standard rules classify them as insoluble in water.

Information gathered from public forums or data available on the internet and portrayed here.