Solids reacting with acids to evolve gas

Steps:

• Recall that dilute HCl reacts with bases, carbonates, and some metals to produce gases like H2, CO2, or Cl2.
• Test each option: acids neutralize oxides/bases without gas; carbonates produce CO2; metals vary by reactivity.
• Eliminate non-reactive solids like carbon and copper, which don't produce gas with dilute HCl.
• Confirm sodium carbonate effervesces CO2 with acids.

Why D is correct:

• Sodium carbonate (a carbonate) reacts with dilute HCl via Na2CO3 + 2HCl → 2NaCl + H2O + CO2(g), producing carbon dioxide gas.

Why the others are wrong:

• A. Carbon is inert and does not react with dilute HCl to produce any gas.
• B. Copper is below hydrogen in the reactivity series and does not displace H2 from dilute HCl.
• C. Magnesium oxide is a base that neutralizes HCl to form salt and water (MgO + 2HCl → MgCl2 + H2O), with no gas evolved.

Final answer: D