Chlorine dioxide can revert to chlorite and chlorate under which conditions?

• A. Lower pH, Low Temperature, Hypochlorite Ion and Sodium Chlorite
• B. Higher pH, Low Temperature, Hypochlorite and Sodium Chlorite
• C. Higher pH, High Temperature, Chlorite and Chlorate
• D. Lower pH, High Temperature, Chlorine Gas and Chlorate

Answer: (C)

Chlorine dioxide becomes unstable in alkaline, hot conditions and tends to undergo disproportionation to form chlorite and chlorate. Disproportionation is when a single species is simultaneously reduced and oxidized to two different species, so ClO2 is converted into ClO2− (chlorite) and ClO3− (chlorate). Raising the pH (more basic conditions) and increasing temperature accelerate this process, making chlorite and chlorate the likely byproducts. That’s why the scenario with higher pH and higher temperature producing chlorite and chlorate is the best match. Acidic conditions or different products (like chlorine gas or hypochlorite) don’t reflect this pathway, so they aren’t correct.