Final answer:
The atomic-level phenomenon occurring when a metal undergoes pressure, like a blow from a hammer, is that the metal cations easily slide past one another.
Step-by-step explanation:
The best description of the atomic-level phenomenon occurring when a metal undergoes pressure, like a blow from a hammer, is option b) The metal cations easily slide past one another.
When a force is applied to a metal, the free-flowing electrons can slip in between the stationary cations and prevent them from coming in contact.
This allows the metal cations to move and slide past each other, resulting in the metal's ability to be malleable and ductile.
This sliding motion of the metal cations is similar to ball bearings coated with oil sliding past one another. It is this property that allows metals to be shaped and formed into various objects through processes like hammering, rolling, and wire drawing.