D

Cobalt-chromium casting alloys are much stiffer than gold alloys (E ≈ 210 GPa, about twice that of type IV gold) and therefore more rigid. They exhibit very low elongation and are considered brittle, so their ductility is lower, not higher, than gold alloys. In addition, their yield/proportional limit is actually higher than that of gold alloys, not lower. Thus statement D is the single incorrect option. [Morris, 1990, PMID 2329540]