Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations Na⁺ and hydroxide anions OH⁻.Sodium hydroxide is a highly corrosive base and alkali that decomposes lipids and proteins at ambient temperatures and may cause severe chemical burns. It is highly soluble in water, and readily absorbs moisture and carbon dioxide from the air. It forms a series of hydrates NaOH·nH₂O. The monohydrate NaOH·H₂O crystallizes from water solutions between 12.3 and 61.8 °C. The commercially available “sodium hydroxide” is often this monohydrate, and published data may refer to it instead of the anhydrous compound.Sodium hydroxide 0.1 is a strong base and highly caustic solution with a concentration of 0.1 mol/L or 0.1 N. Sodium hydroxide 0.1 may be corrosive to metals. It should be kept in its original container and any spillage should be absorbed to prevent material damage.