Final answer:
True, iron rusts when exposed to oxygen and moisture; both elements are required for rust to form, and rust is a type of corrosion.
Step-by-step explanation:
The statement that rusting of iron will occur when it is placed in open air or in moisture is true. Rusting is a form of corrosion where iron combines with oxygen and water in the environment to form a red-brown hydrated metal oxide known as rust (Fe₂O₃·xH₂O).
For rust to form, the presence of both oxygen and water is essential. Therefore, an iron nail will not rust if it is immersed in deoxygenated water or an organic solvent like kerosene or mineral oil, which lacks water, even if oxygen is present. The process of rusting involves the initial oxidation of iron to iron (II) ions at an anodic site on the metal surface, often at an impurity or defect, followed by further oxidation to form rust.