Substance X as Barium Metal from Reaction Products

Steps:

• Substance X reacts with water to produce a gas (hydrogen) and increase pH, indicating a reactive metal forming a basic hydroxide solution.
• The solution, containing metal hydroxide ions, reacts with sulfuric acid to form a white precipitate, identifying an insoluble sulfate like BaSO4.
• Barium metal fits: Ba + 2H2O → Ba(OH)2 + H2 (gas, basic solution).
• Adding H2SO4 to Ba(OH)2 yields BaSO4 precipitate, confirming barium.

Why A is correct:

• Barium metal reacts with water per the equation Ba + 2H2O → Ba(OH)2 + H2, producing gas and base; Ba2+ forms white, insoluble BaSO4 with H2SO4.

Why the others are wrong:

• B: Barium oxide (BaO + H2O → Ba(OH)2) produces no gas with water.
• C: Magnesium oxide (MgO + H2O → Mg(OH)2) produces no gas; MgSO4 is soluble, no precipitate.
• D: Identical to C, magnesium oxide fails both tests.

Final answer: A