1. . 
The compound with the formula CO2. An odorless gas, carbon dioxide [CO2] is widely distributed in nature and is a minor component of air. It is highly soluble in water and oil, especially under pressure. In water, it occurs as carbonic acid, a weak acid that can donate one or two hydrogen ions in neutralization reactions that produce bicarbonate [HCO3–] and carbonate [CO3–2] salts or ions. CO2, being an acid in water, reacts instantly with NaOH or KOH in an alkaline water mud, forming carbonate and bicarbonate ions. Similarly, it reacts with Ca(OH)2 (lime) to form insoluble calcium carbonate and water.