Acid-metal reaction producing hydrogen gas effervescence

Steps:

• Effervescence signals gas release; with dilute organic acid solution, adding reactive metal like Mg produces H₂.
• Organic compound P is CH₃COOH(aq) at 0.1 mol/dm³, a weak acid that reacts with metals.
• Solid added is Mg(s), displacing hydrogen from the acid.
• Verify balance: Option A correctly shows 2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂.

Why A is correct:

• Equation balances atoms (C:4, H:8, O:4, Mg:1) and uses correct formula for divalent Mg salt (CH₃COO)₂Mg per ionic compound rules.

Why the others are wrong:

• B: Incorrect salt formula CH₃COOMg (should be (CH₃COO)₂Mg); unbalanced carbon and hydrogen atoms.
• C: Wrong salt formula (CH₃COO)₂K (potassium acetate is CH₃COOK); unbalanced potassium (2 left, 1 right).
• D: K₂CO₃(s) is highly soluble in water, unlike the insoluble metal solid implied for sustained effervescence.

Final answer: A