Calcium carbonate neutralizes acidic pollutants

Steps:

• Calcium carbonate (CaCO3) reacts with acidic gases to form salts and carbon dioxide.
• Sulfur dioxide (SO2) is an acidic oxide that reacts: CaCO3 + SO2 → CaSO3 + CO2.
• Nitrogen dioxide (NO2) is also acidic and reacts similarly: 2NO2 + CaCO3 → Ca(NO3)2 + CO2 (in moist conditions).
• Methane (CH4) and unburned hydrocarbons are neutral or non-acidic, so they do not react.

Why B is correct:

• SO2 and NO2 are acidic oxides neutralized by CaCO3 in flue gas desulfurization and denitrification processes.

Why the others are wrong:

• A: Methane (2) is inert and does not react with CaCO3.
• C: Neither methane (2) nor hydrocarbons (4) are acidic.
• D: Hydrocarbons (4) do not react with CaCO3.

Final answer: B