Step 1: Analyzing Statement A. Pyrite (\(FeS_2\)), a sulfide mineral, oxidizes in air and water, forming sulfuric acid (\(H_2SO_4\)). This process, acid mine drainage, increases soil and water acidity. Statement A causes acidity.
Step 2: Analyzing Statement B. The aluminum extraction process (Bayer process) uses hot sodium hydroxide (a strong base) to digest bauxite ore. The waste, red mud, is alkaline, not acidic. Statement B does not cause acidity.
Step 3: Analyzing Statement C. Ammonium-based nitrogen fertilizers can cause soil acidity via nitrification. Soil bacteria convert ammonium (\(NH_4^+\)) to nitrate (\(NO_3^-\)), releasing hydrogen ions (\(H^+\)), thus lowering soil pH. Statement C causes acidity.
Step 4: Analyzing Statement D. Limestone, calcium carbonate (\(CaCO_3\)), is an alkaline material used to neutralize soil acidity by reacting with \(H^+\) ions. It treats acidity, not causes it. Statement D does not cause acidity.
Conclusion: Statements A and C cause soil acidity.