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, photography, and medicine.
In photography, sodium thiosulfate is used as a fixing agent. It reacts with the unexposed silver halide in the photographic film or paper, converting it into a soluble salt that can be washed away. This leaves behind only the exposed silver halide, which is then developed into a permanent image.
Sodium thiosulfate is also used in the production of photographic paper and film. It is added to the emulsion to help prevent the formation of fog. It is also used to stabilize the emulsion and to improve its sensitivity to light.
In medicine, sodium thiosulfate is used as an antidote for cyanide poisoning. It reacts with cyanide to form thiocyanate, which is a less toxic compound. Sodium thiosulfate is also used to treat methemoglobinemia, a condition in which the blood is unable to carry oxygen. It does this by converting methemoglobin back into hemoglobin.
Sodium thiosulfate is a safe and effective compound that has a wide range of applications. It is an essential part of the photographic process and is also used in medicine to treat a variety of conditions.
The other options are incorrect because they are not used in photography. Sodium tetrahionate is a white, water-soluble solid that is used as a bleaching agent. Sodium sulfate is a white, water-soluble solid that is used in a variety of applications, including the production of paper, glass, and detergents. Ammonium persulfate is a white, water-soluble solid that is used as a bleaching agent and a disinfectant.