Question

all of the following compounds are insoluble except
○ pbso₄
○ mgso₄
○ cuco₃
○ hg₂cl₂

Explanation:

Step1: Recall solubility rules

• Chloride ($Cl^-$) salts: Most chloride salts are soluble. However, $Hg_2Cl_2$ is insoluble.
• Carbonate ($CO_3^{2 - }$) salts: Most carbonate salts are insoluble. So, $CuCO_3$ is insoluble.
• Sulfate ($SO_4^{2 - }$) salts: Most sulfate salts are soluble. But $PbSO_4$ is insoluble.
• $MgSO_4$: Magnesium sulfate is soluble as per the solubility rules for sulfate salts (magnesium is not one of the exceptions like lead, calcium (slightly soluble), barium etc.).

Answer:

$MgSO_4$