Which combination is the empirically known set of conditions (Inoue's empirical rules) for alloys that readily form bulk metallic glasses, which become glass even at thicknesses of several mm or more?

Answer: C. It has three or more elements, with main-element atomic radii differing by about 12% or more and a negative heat of mixing

Inoue's empirical rules are three: multiple components, an atomic radius difference of about 12% or more among the main elements, and a negative heat of mixing. When atoms of different sizes mix while attracting one another, the liquid takes a densely packed, disordered arrangement, and atomic diffusion and rearrangement slow down. In addition, forming a crystal from a liquid containing many elements requires extensive rearrangement of atoms, so crystal nucleation and growth become difficult. A lower liquidus temperature at compositions near a deep eutectic also helps. Combinations with equal atomic radii and positive heat of mixing tend to form solid solutions or phase-separate, and compositions close to a pure metal hardly become glass even with quenching at about 10⁶ K/s.