Which of the following reactions will produce a gas?

• A. BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)
• B. NaCl(aq) + AgNO₃(aq) → AgCl(s) + NaNO₃(aq)
• C. CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
• D. HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

Answer: (C)