Pure carbon is a relatively reactive element and combines directly with many chemical elements, especially those considered oxidizing agents. Carbon has a particularly strong affinity for oxygen either in the form of gaseous oxygen, or as oxygen contained in chemical combination with other elements. Its ability to combine with oxygen makes it both a powerful and useful reducing agent (a substance that donates electrons resulting in reduction of the charge of the ion or atom being reduced). As an example, solid carbon is used to reduce iron from its oxide (Fe(+3) to Fe(0) )in the blast furnace or other similar processes in which metallic elements are reduced from their oxide ores.