Nickel(II) oxide is a chemical compound with the formula NiO. It consists of nickel in the +2 oxidation state and oxygen. This compound appears as a greenish-black solid and is commonly used in ceramics, glass, and as a catalyst in various chemical reactions. In addition to its industrial applications, nickel(II) oxide is also studied for its potential use in batteries and fuel cells. It can be produced through the thermal decomposition of nickel hydroxide or by reacting nickel salts with alkaline solutions. Safety precautions are necessary when handling this compound, as it can be toxic if ingested or inhaled.