Disproportionation of Cl2 in alkaline conditions to achieve +5 oxidation state

Steps:

• Target +5 oxidation state for Cl occurs in chlorate ion, ClO3-.
• Cl2 undergoes disproportionation with NaOH; conditions determine products.
• Cold dilute NaOH yields Cl- (oxidation state -1) and ClO- (+1).
• Hot concentrated NaOH yields Cl- (-1) and ClO3- (+5).

Why D is correct:

• Hot concentrated NaOH reacts via 3Cl2 + 6NaOH → 5NaCl + NaClO3 + 3H2O, oxidizing some Cl from 0 to +5 in ClO3-.

Why the others are wrong:

• A: Tests Cl- ions by forming AgCl precipitate, soluble in NH3; no oxidation of Cl2.
• B: Cl2 inert to concentrated H2SO4 at room temperature; no reaction to +5 state.
• C: Cold dilute NaOH gives Cl2 + 2NaOH → NaCl + NaClO + H2O, max +1 oxidation state in ClO-.

Final answer: D