Question 6
Which metal, though more reactive than iron, does not tarnish under ordinary atmospheric conditions?
The right answer is the one marked above.
Aluminium (Al). It stands above iron in the activity series, yet aluminium articles need no special measures to keep them from tarnishing.
Copper, silver and gold are all less reactive than iron, so they do not fit the question. The thin oxide layer that forms at once on aluminium protects the metal beneath.