The problem with using brittle metals is that:

Brittle metals are characterized by their inability to deform plastically when subjected to stress. This means that instead of bending or deforming under pressure, they can fracture suddenly and without warning. This quality poses significant risks in applications where sudden failure could lead to catastrophic outcomes, such as in refrigeration systems where components may experience varying stress loads.

In contrast, while the other options touch on attributes of metals, they do not accurately reflect the primary concern with brittleness. For example, ductility, which is the capacity to endure deformation without breaking, is a more relevant factor when discussing metal strength. Understanding these qualities helps in selecting suitable materials for specific applications in refrigeration and other engineering fields.