Oxidation numbers in ICl and Cl-O anions from reactions

Steps:

• Assign oxidation numbers in ICl: I (less electronegative) is +1 (x), Cl is -1 (y), as the sum is zero.
• Note reaction ICl + 2NaOH → NaOI + NaCl + H2O preserves x = +1 for I in IO⁻ and y = -1 for Cl in Cl⁻.
• Identify chlorate ion from Cl₂(aq) + cold dilute NaOH(aq) as ClO⁻ (hypochlorite, often called chlorate(I)), where Cl oxidation number is +1.
• Recognize no Cl-O anion (chlorate) forms from Cl⁻(aq) + NaOH(aq), as Cl⁻ requires oxidation not provided by OH⁻.

Why A is correct:

• x = +1 matches Cl oxidation number (+1) in ClO⁻ formed by Cl₂ disproportionation in NaOH, per standard naming for oxyanions.

Why the others are wrong:

• B: No chlorate ion forms from Cl⁻ + NaOH, so no comparable oxidation number.
• C: y = -1 differs from +1 for Cl in ClO⁻ from Cl₂ + NaOH.
• D: No chlorate ion from Cl⁻ + NaOH, invalidating comparison.

Final answer: A