Arsenic trioxide, with the chemical formula As2O3, is a chemical compound composed of arsenic (As) and oxygen (O) atoms. It is also known as white arsenic or arsenic(III) oxide. Arsenic trioxide occurs naturally as the mineral arsenolite and can also be produced industrially as a white powder.

Arsenic trioxide has been used historically for various purposes, but its use has significantly declined due to its high toxicity. Some key properties and uses of arsenic trioxide include:

1. Medicinal Use: Historically, arsenic trioxide was used in traditional medicine for various ailments. It was also used as a component of certain medical formulations, such as Fowler’s solution, which was once prescribed for a wide range of conditions. However, its use in medicine has largely been abandoned due to its toxic effects and the availability of safer alternatives.
2. Wood Preservative: Arsenic trioxide was historically used as a wood preservative to protect against decay and insect infestation. However, its use in this application has been phased out in many countries due to environmental and health concerns.
3. Insecticide: It was used as an insecticide in the past. However, similar to wood preservation, its use as an insecticide has been limited due to its toxicity and environmental impact.
4. Research and Laboratory Studies: Arsenic trioxide is still used in research and laboratory studies as a chemical reagent and for its toxicological properties.

Due to its extreme toxicity, arsenic trioxide is considered a hazardous substance, and exposure to it should be avoided. Proper safety measures, such as good ventilation and the use of personal protective equipment, should be followed when working with arsenic trioxide or any arsenic-containing materials.

In modern times, arsenic trioxide is mostly used in research and laboratory settings and has limited practical applications due to its toxicity and potential health risks.