Why did vinegar and salt solution clean the pennies?

Vinegar, which contains acetic acid, reacts with the copper oxide and other tarnish on the pennies, helping to dissolve the oxidation. Salt acts as an abrasive and enhances the reaction by facilitating the transfer of electrons, effectively aiding the acid in breaking down the tarnish. Together, this solution cleans the pennies by removing the dull surface layer, restoring their shine.