Question

Which of the following sets of coinage metals?
(A) Cu, Ag, Au
(B) Zn, Cd, Hg
(C) Au, Ag, Zn
(D) Li, Na, K

Answer 1

Hint:
Coinage metals are those metals which are used or were used earlier to make coins. Set of coinage metals means the alloy of the respective set of metals. Generally less reactive metals are used in production of coins.

Complete answer:
- Coinage metals are those metals which are used or were used earlier to make coins. The metals are mixed to form an alloy and this alloy is used to make the coins.
- So, we now need to find which metals are used to make coins. It is a basic requirement of a metal to be a part of an alloy that it should be less reactive to atmosphere because if it would react, then the coin will change its appearance and characteristics.
- Alkali metals are very reactive to water and other species as they have only one electron in its valence shell. So, they are not used in coins.
- Mercury is also toxic as well as reactive metal. So, it can not be used in the formation of coins.
- Other two options show Ag, Au, Cu and Ag, Au and Zn. Here only Zn and Cu differ from the two sets. Now copper is cheap and also not reactive and is being used from ancient times to produce coins. So, Copper will be the right choice with Au and Ag to make coins.
Hence correct answer is (A) Cu, Ag, Au

Additional Information:
- It is required for a coinage metal to have excellent resistance to environmental changes and corrosion.
- However the exact definition of coinage metals do not exist.
- There are such other elements like iron, chromium, tin, platinum and zinc that are used as one of the components in the alloy of coins.

Note:
Remember that Alkali metals are not stable and very reactive, so they cannot be used in the production of coins. Zn is more reactive metal than copper so it is not preferred over copper but even though its reactivity, it is used sometimes in coins.