Because it reacts easily with oxygen in the air to produce crumbly red iron oxides. 因为它非常容易和空气中的氧气起反应，生成易碎的红色氧化铁。
In other words, iron has a strong tendency to rust if exposed to air and damp, for iron and oxygen make rust, or red oxide of iron. 换言之，铁如果接触空气和湿气特别容易生锈，因为铁与氧化合成锈或红色的氧化铁。
