The apparent discrepancy you're describing can be attributed to the concept of density. Density is a measure of how much mass is contained in a given volume. Different materials have different densities, which means that even if they have the same mass, they can take up different amounts of space (volume) due to their varying densities.
Copper and gold have different densities, with gold being denser than copper. This means that a given mass of gold occupies less volume compared to the same mass of copper. In other words, gold is more "compact" in terms of how its atoms are arranged, resulting in a higher density.
So, when you say a 10-gram piece of copper takes up more space than a 10-gram piece of gold, you're actually observing the effect of their densities on their volumes. The copper piece is less dense, so it needs more space to contain the same mass as the denser gold piece.
I hope this helped!
~~~Harsha~~~