Disproportionation of chlorine in water

Steps:

• Assign oxidation states: In Cl₂, Cl is 0; in HOCl, Cl is +1 (H +1, O -2); in HCl, Cl is -1.
• Identify changes for Cl: Some Cl atoms go from 0 to +1 (oxidation, loss of electrons); others from 0 to -1 (reduction, gain of electrons).
• Check hydrogen: In H₂O and HCl, H remains +1 (no change in oxidation state).
• Conclude: Cl undergoes both processes, while H does not; this is disproportionation.

Why A is correct:

• Chlorine is both oxidized (0 to +1 in HOCl) and reduced (0 to -1 in HCl), per the definition of disproportionation where one element is simultaneously oxidized and reduced.

Why the others are wrong:

• B: Chlorine is also reduced (to -1 in HCl), not solely oxidized.
• C: Hydrogen's oxidation state stays +1 in both H₂O and HCl, so neither process occurs.
• D: Hydrogen experiences no oxidation or reduction.

Final answer: A