Potassium arsenite is a chemical compound. Its chemical formula is KAsO2. It has potassium and arsenite ions in it.
It is a solid. It is highly toxic.
It is made by reacting arsenic trioxide with potassium hydroxide.
It was used as a "medicine", but it is carcinogenic and toxic so it is not used anymore. It is banned for use as a pesticide in the United Kingdom.