Correct reaction of HCl with carbonates

Steps:

• Identify acid-carbonate reaction: produces salt, water, and carbon dioxide gas.
• Verify option A: MgCO₃ + 2HCl → MgCl₂ + H₂O + CO₂ (three products).
• Check option B: Mg + 2HCl → MgCl₂ + H₂ (hydrogen, not water).
• Confirm options C and D: Acid addition keeps indicator colorless; no NH₃ from NH₄Cl + HCl.

Why A is correct:

• Carbonates react with acids per the general equation: metal carbonate + acid → salt + water + CO₂, forming three products.

Why the others are wrong:

• B: Metal-acid reaction produces hydrogen gas, not water (Mg + 2HCl → MgCl₂ + H₂).
• C: Thymolphthalein is colorless in acidic conditions (pH < 9.3), so it stays colorless.
• D: NH₄Cl + HCl forms no ammonia; NH₃ requires a base like NaOH to displace it.

Final answer: A