Iron will not rust if kept in a vacuum. Rusting is a chemical reaction that occurs when iron or steel comes into contact with oxygen and moisture in the presence of an electrolyte (such as water). In a vacuum, the absence of oxygen and moisture prevents the rusting process from taking place.
In a typical environment, iron or steel objects are exposed to air and moisture, which allows oxygen and water molecules to react with the iron's surface, forming iron oxide (rust). However, in a vacuum, the absence of air and moisture prevents this reaction, effectively halting the rusting process.
So, if you were to keep iron in a completely sealed and air-tight vacuum environment, it would not rust. However, it's essential to ensure the vacuum remains completely sealed to prevent any air or moisture from entering and causing rust in the future.