Question

Why are alloys used to make coins rather than the pure metal?

Answer 1

Pure metals tend to be softer and wear faster. Actually, the penny is (since 1982) 97.5% zinc, but with a thin coating of copper to make it look like the original 95% copper pennies. Other US coins (except the seldom-used dollar)are a copper-nickel alloy, which is stronger and more "silver-like" in appearance than pure nickel or copper.
The dollar coin consists of four metals in a bronze sandwich structure, with maganese added to copper, zinc and nickel in the surface layers