Solubility of Group 2 hydroxides and sulfates determines residue and precipitate

Steps:

• Shake mixture with water: Group 2 oxide reacts to form hydroxide; soluble hydroxide enters filtrate, insoluble sulfate remains as residue.
• Filter: Solid residue is insoluble sulfate (e.g., BaSO4); filtrate contains dissolved hydroxide (e.g., Ba(OH)2).
• Add H2SO4 to filtrate: Soluble barium hydroxide forms insoluble BaSO4 white precipitate; magnesium hydroxide is insoluble, so no precipitate from its filtrate.
• Identify mixture: Only BaO + BaSO4 yields residue and white precipitate in filtrate.

Why A is correct:

• Ba(OH)2 (soluble) in filtrate reacts with H2SO4 to form BaSO4 (insoluble white precipitate), per solubility rules for Group 2 compounds.

Why the others are wrong:

• B: Filtrate is MgSO4 (soluble); no precipitate with H2SO4.
• C: Both Ba(OH)2 and MgSO4 soluble; no solid residue obtained.
• D: Filtrate empty (both Mg(OH)2 and BaSO4 insoluble); no precipitate forms.

Final answer: A