Is there any options or is it paragraghs??
2, 3, and 5 is the answer, good luck with your work :D
Here's what's happening: The oxygen in the air and the copper in the pennies form an oxide that coats the pennies and makes them look dirty. The acids (usually vinegar - acetic acid) break the copper oxide free from the penny. As we have seen experimentally, acid alone does not clean as well as acid and salt.
