Chlorine Disproportionation in Alkaline Conditions

Steps:

• Reaction 1 with cold NaOH: Cl₂ disproportionates to hypochlorite (ClO⁻) and chloride (Cl⁻), so Z is ClO⁻; equation is Cl₂ + 2OH⁻ → ClO⁻ + Cl⁻ + H₂O.
• Reaction 2: Heating Z (ClO⁻) causes further disproportionation to chlorate (ClO₃⁻) and Cl⁻; equation is 3ClO⁻ → ClO₃⁻ + 2Cl⁻ (assuming question intends ClO₃⁻, not ClO⁻, as latter mismatches chemistry).
• Eliminate choices with incorrect reaction 1 (hot NaOH or unbalanced).
• Select choice matching both standard equations.

Why C is correct:

• Equations follow established disproportionation formulas for cold NaOH (hypochlorite formation) and hypochlorite heating (chlorate formation).

Why the others are wrong:

• A: Reaction 1 stoichiometry wrong (2Cl₂ + 2OH⁻ unbalanced, produces excess Cl).
• B: Reaction 1 for hot concentrated NaOH (forms ClO₃⁻ directly); reaction 2 unbalanced and incorrect products.
• D: Reaction 2 unbalanced (charge/O atoms mismatch) and wrong products (no ClO₃⁻).

Final answer: C