Which preventive method can be used to stop iron from rusting?

Using grease and oil as a preventive method to stop iron from rusting is effective because these substances create a hydrophobic (water-repelling) barrier on the surface of the iron. Rusting is an electrochemical process that requires moisture and oxygen to occur. By applying grease or oil, the surface of the iron is coated, preventing water and oxygen from coming into contact with the metal. This significantly reduces the chance of oxidation and subsequent rust formation.

Other methods, while they may offer some level of protection, do not directly address moisture and oxygen exposure as effectively as grease and oil do. For example, heat treatment can alter the properties of iron but does not prevent rusting. Electrolysis is more of a method for removing rust than preventing it, and carbon coating can be complex and may not provide comprehensive protection against rust. Therefore, using grease or oil remains one of the most straightforward and effective means to protect iron from rusting.