We can actually see here that the evidence that we have that zinc was added to change the coin from copper to silver is seen when a solution of sodium hydroxide is mixed with zinc dust and heated. The zinc is seen to dissolve in the copper coin in small amounts. This makes the coin to change from copper to silver.
The silver-colored coin changes to gold when the silver-colored coin is placed on the surface of a hot plate. The brass alloy coating on the coin then turns to a golden color. This is actually a chemical change.
What is a chemical change?
Chemical change is actually known to be the change that occurs when one chemical substance reacts or combines with another substance in order to form a new substance. This process are not usually reversible except further chemical reactions are carried.
Thus, the above answers for the question are correct.
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