Answer: homogenus mixture.
Justification:
1) Coins are made of metal alloys.
2) Alloys are mixtures of metals or of a metal and non-metals.
3) When the alloy is in the form of a solid solution of metal elements, like in the coin case, it can be compared to a liquid solution in the sense that they both constiture a homogeneous mixture.
4) A heterogeneous mixture means that the constituents of the mixture are in different phases, nor uniformily distributed, and you can distinguish them easily (normally visually).
So, you can affirm that they are homogeneous mixtures.