Answer:
i) Rusting occurs the least in tubes 2 and 3 because either of air and water which are necessary for rusting is absent in the two tubes respectively.
ii) Rusting occurs most in tube 1 because both air and water which are necessary for rusting are present.
Explanation:
Rusting is a chemical change which involves a redox reaction. During the process of rusting, metallic iron is oxidized to hydrated iron (iii) oxide by oxygen present in air.
For rusting to take place effectively, each of these three factors mist be available: metallic iron, oxygen and water.
In the figure above, the iron nails in the three tester tubes will rust to different extents based on the availability of the three factors.
In test tube 1, the iron nails will rust the most because all the three factors: metallic iron, oxygen present in air, and water are abundantly present.
In test tube 2, the iron nails will rust the least or not at all because boiling of water removes dissolved oxygen from water and the oil layer above the boiled water prevents entry of oxygen from air. Thus, the nail do not rust because one of the three factors for rusting to take place, in this instance, oxygen is absent.
In test tube 3, the iron nails rusts the least or not at all as well because moisture or water is absent. Calcium chloride, a drying agent removes all the moisture from inside the tube. Hence, even though air is present, rusting do not occur as there is no moisture or water present.
