Bleaching action of moist sulfur dioxide is because of its
(1) basic property
(2) acidic property
(3) oxidizing property
(4) reducing property
Answer: (3) In moist conditions, sulfur dioxide is a bleaching agent. In the reducing action of SO2, oxygen is removed from the colored dye. Sulfur dioxide is used to bleach wool and silk. Salts of sulfur dioxide are also used in bleaching. Calcium hydrogen sulfite Ca(HSO3)2 is used to whiten wood pulp in the manufacturing of paper. Other than SO2, sodium hydrosulfite (Na2S2O4) is also used to bleach wool. However, bleaching using SO2 is not permanent. On exposure to air and light, the original color slowly returns as oxygen in air oxidizes the bleached substance.
