Question

write one method of preparation of ClO2

Answer 1

ClO2 made from Sodium Chlorate:

Reduction of Chlorates by Acidification in the Presence of Oxalic Acid  

2 HClO3 + H2C2O4 --> 2 ClO2 + 2 CO2 + 2 2O

Reduction of Chlorates by Sulfur dioxide (Mathieson Process)  

2 NaClO3 + H2SO4 + SO2 --> 2 ClO2 + 2 NaHSO4

Answer 2

Chlorine dioxide is a chemical compound with the formula ClO2. This yellowish-green gascrystallizes as bright orange crystals at −59 °C. As one of several oxides of chlorine, it is a potent and useful oxidizing agent used in water treatment and in bleaching.[4]