The correct answer is C. oxidising property.
Moist sulphur dioxide is a bleaching agent because it reacts with organic compounds to form oxidized products. This reaction is called oxidation, and it is a chemical reaction that involves the loss of electrons. In the case of moist sulphur dioxide, the organic compound loses electrons to the sulphur dioxide, which is oxidized to sulphuric acid. The oxidized product is usually a colorless or light-colored compound, which is why moist sulphur dioxide is a bleaching agent.
A basic property is a property of a substance that can neutralize acids. An acidic property is a property of a substance that can react with bases to form salts. A reducing property is a property of a substance that can donate electrons to another substance.
Moist sulphur dioxide does not have a basic property, because it does not react with acids to form salts. Moist sulphur dioxide does not have an acidic property, because it does not react with bases to form salts. Moist sulphur dioxide does have a reducing property, because it can donate electrons to another substance. However, the bleaching action of moist sulphur dioxide is not due to its reducing property, but rather due to its oxidizing property.