A student screens materials for use in a high-temperature electrical feedthrough. The student uses an operational model in which a bond between a metal and a nonmetal has predominantly ionic character when \(\Delta\chi>1.7\). A bond between two nonmetals is polar covalent when \(0.5\leq\Delta\chi\leq1.7\) and nonpolar covalent when \(\Delta\chi<0.5\). A material composed only of metals is evaluated for metallic bonding by using its conductivity and mechanical behavior.

Sample	Types of constituent elements	Electronegativity values, \(\chi\)	Solid conductivity, \(\sigma\) \((\text{S}\,\text{m}^{-1})\)	Conductivity after melting, \(\sigma\) \((\text{S}\,\text{m}^{-1})\)	Mechanical behavior as a solid
\(\text{MgO}\)	metal and nonmetal	\(1.3,\ 3.4\)	\(<1\times10^{-10}\)	\(3\times10^{2}\)	Shatters under applied force
\(\text{ICl}\)	two nonmetals	\(2.7,\ 3.2\)	\(<1\times10^{-10}\)	\(<1\times10^{-10}\)	Shatters under applied force
\(\text{Cu-Ni}\) alloy	two metals	\(1.9,\ 1.9\)	\(2\times10^{6}\)	\(1\times10^{6}\)	Deforms without shattering

Which assignment of dominant bonding character is most consistent with both the model and the data?