When analyzing machinery, which of the following would indicate a problem with corrosion?

The correct answer, which indicates a problem with corrosion, is the presence of tin. Tin is often used as a coating for other metals to prevent corrosion, specifically in the food canning industry. However, if tin is present in areas where it has corroded, it may indicate that the substrate it protects is experiencing corrosion.

While aluminum, iron, and magnesium can all corrode, their presence alone does not specifically indicate a corrosion issue. Aluminum typically forms a protective oxide layer that prevents further corrosion, and magnesium, while prone to corrosion, is commonly used in applications where weight is a critical factor. Iron, on the other hand, is well-known for rusting, but its presence in an analysis does not directly signal an issue unless it shows signs of corrosion, such as rust formation. Thus, the detection or inquiry about tin can be a viable indication that corrosion has influenced the materials in machinery.