Halogen reactivity and oxidation by sulfuric acid

Steps:

• Halogens follow reactivity order Cl > Br > I; more reactive displaces less reactive from compounds.
• Concentrated H2SO4 reacts with NaCl to form HCl, not oxidizing Cl- to Cl2.
• With NaBr, H2SO4 first forms HBr, then oxidizes it to Br2 due to Br- being more easily oxidized than Cl-.
• I2 cannot displace Br- from NaBr as I is less reactive.

Why C is correct:

• Concentrated H2SO4 oxidizes Br- to Br2 via 2HBr + H2SO4 → Br2 + SO2 + 2H2O, liberating bromine gas.

Why the others are wrong:

• A: Br2 cannot displace Cl2 from NaCl as Cl is more reactive than Br.
• B: Conc H2SO4 with NaCl yields HCl gas, not oxidizing Cl- to Cl2.
• D: I2 in KI(aq) cannot displace Br- from NaBr as I is less reactive than Br.

Final answer: C