Chlorine reactions producing sodium chlorate

Steps:

• Recall Cl2 + 2NaOH (cold, dilute) → NaCl + NaClO + H2O, yielding hypochlorite.
• Recall 3Cl2 + 6NaOH (hot, concentrated) → 5NaCl + NaClO3 + 3H2O, yielding chlorate.
• Recall Cl2 + 2NaBr → 2NaCl + Br2, a displacement reaction with no oxygen compounds.
• Conclude only the hot NaOH reaction produces NaClO3.

Why B is correct:

• The formula 3Cl2 + 6NaOH (hot, concentrated) → 5NaCl + NaClO3 + 3H2O defines the condition for sodium chlorate formation.

Why the others are wrong:

• A: Cold NaOH forms NaClO (hypochlorite), not NaClO3.
• C: Forms NaCl and Br2 via halide displacement, no chlorate.
• D: Not enough information.

Final answer: B