Concentrated H2SO4's dual role as acid and oxidant with halides Steps: - Concentrated H2SO4 acts as a strong acid in proton transfer reactions and as an oxidizing agent by reducing to SO2. - With magnesium carbonate, it only decomposes via acid-base reaction: MgCO3 + H2SO4 → MgSO4 + H2O + CO2, no oxidation. - With potassium chloride, it forms HCl but does not oxidize Cl- to Cl2 due to insufficient oxidizing power. - With potassium bromide, it first acts as acid to form HBr, then oxidizes Br- to Br2: 2KBr + H2SO4 → K2SO4 + 2HBr; 2HBr + H2SO4 → Br2 + SO2 + 2H2O. - With sulfur trioxide, it absorbs to form oleum (H2S2O7), neither acid-base nor redox. Why C is correct: - KBr undergoes acid displacement to HBr followed by oxidation to Br2, per the redox half-reaction: 2Br- → Br2 + 2e-, with H2SO4 reduced to SO2. Why the others are wrong: - A: Reacts only as acid to evolve CO2, no redox. - B: Forms HCl but no oxidation of Cl- to Cl2. - D: Forms pyrosulfuric …