Which of the following is a barrier method to prevent rust on iron?

• A. Paint
• B. Oil
• C. Grease
• D. Salt

Answer: (A)

Rust happens when iron is exposed to oxygen in the presence of water. A barrier method stops rust by keeping air and moisture away from the metal. Painting iron creates a film that sits on the surface and blocks both oxygen and water from reaching the iron, so oxidation can’t start. Oil or grease can act as a barrier too, but they’re easier to remove and don’t protect as reliably over time. Salt isn’t a barrier; it makes the environment more conductive and can speed up corrosion. So painting is the best barrier method here.