A DEADIY COMPOUND Hydrogen cyanide (HCN) is a poisonous pas found in the exhaust of vehicles, in tobacco and wood smoke, and in smoke from burning Write the ionization equations for HCN. nitrogen-containing plastics. Some insects such as millpedes and bumet moths release hydrogen cyanide as a defense mechanism. A solution of bydrogen cyanide in water is called tydrocyaric acid. Fruits that have a pit, such as cherries or peaches, cortain cyanohydrins, which convert to hydrocyenic acid in the digestive system id the pits are eaten, However, no hydrocyanic acid is produced in the flesh of these fruits, so the fruit can safely be eaten