I want to test the ability of students to read a passage and answer questions about it. Could you please come up with a good question for the passage "An alloy is a mixture of metals or a mixture of a metal and another element. Alloys are defined by metallic bonding character. An alloy may be a solid solution of metal elements (a single phase) or a mixture of metallic phases (two or more solutions). Intermetallic compounds are alloys with a defined stoichiometry and crystal structure. Zintl phases are also sometimes considered alloys depending on bond types (see also: Van Arkel-Ketelaar triangle for information on classifying bonding in binary compounds)."? 

Which of the following may not be an alloy: intermetallic compounds, Zintl phases, or a mixture of metals?