Describe an experiment that demonstrates the necessity of both air and water for the rusting of iron.

One experiment involves placing an iron nail in three different test tubes. In the first test tube, the nail is submerged in water without exposure to air. In the second test tube, the nail is exposed to air but kept dry. The third test tube contains a nail submerged in water and exposed to air. After a few days, only the nail in the third test tube will show rusting, indicating that both air and water are required for rusting to occur.

This question tests the student's understanding of the conditions necessary for rusting, a key concept in corrosion. The answer clearly outlines a method to observe the effects of air and water on rusting, demonstrating practical application of theoretical knowledge.