The correct answer is A. Sodium thiosulfate.
Sodium thiosulfate is a chemical compound with the formula Na2S2O3. It is a white, water-soluble solid that is used in a variety of applications, including photography, as a reducing agent, and in the manufacture of paper and textiles.
In photography, sodium thiosulfate is used to fix the image on a photographic film or plate. It does this by converting the unexposed silver halide crystals into soluble silver thiosulfate, which is then washed away. This prevents the unexposed silver halide crystals from developing into an image when the film or plate is developed.
Sodium thiosulfate is also used as a reducing agent in a variety of chemical reactions. It is used to reduce metals from their oxides, to convert aldehydes to alcohols, and to convert ketones to carboxylic acids.
In the manufacture of paper and
textiles, sodium thiosulfate is used as a bleaching agent. It is used to bleach the wood pulp that is used to make paper, and to bleach the cotton that is used to make textiles.Sodium thiosulfate is a safe and non-toxic compound. It is not considered to be a hazardous substance. However, it can be irritating to the skin and eyes if it is not handled properly.