GRE Reading Comprehension

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Source: XDF

Calculations of the density of alloys based on Bernal-type models of the alloy's metal component agreed fairly well with the experimentally determined values from measurements on alloys consisting of a noble metal together with a metalloid, such as alloys of palladium and silicon, or alloys consisting of iron, phosphorus, and carbon, although small discrepancies remained. One difference between real alloys and the hard spheres used in Bernal models is that the components of an alloy have different sizes, so that models based on two sizes of spheres are more appropriate for a binary alloy, for example. The smaller metalloid atoms of the alloy might fit into holes in the dense, random-packed structure of the larger metal atoms.

Question List: 1

The author's speculation about the appropriateness of models using spheres of two sizes for binary alloys would be strongly supported if models using spheres of two sizes yielded

  • A values for density identical to values yielded by one-sphere models using the smaller spheres only
  • B values for density agreeing nearly perfectly with experimentally determined values
  • C values for density agreeing nearly perfectly with values yielded by models using spheres of three sizes
  • D significantly different values for density depending on the size ratio between the two kinds of spheres used
  • E the same values for density as the values for appropriately chosen models that use only medium-sized spheres

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