Some properties of Au, Ag and Cu are given below:
Element Metallic radius (pm) m.pt 0°C Common oxidation State
Cu 128 1085 +2
Ag 144 961 +1
Au 144 1064 +3
To make Au stronger and harder, it is often alloyed with other metals such as Cu and Ag. Consider two alloys, one of Au & Cu and the other Au & Ag, each with same mole fraction of Au. If Au/Cu alloy is harder than the Au/Ag alloy then which of the following is the best explanation based on the information in the table above?

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Cu has two common oxidation states, but Ag has only one

Cu atoms are smaller than Ag atoms

Cu atoms are less polarizable than Au or Ag atoms thus Cu has weaker inter particle forces

Cu has a higher m.pt than Au, but Ag has a lower m.pt than Au

answer is C.

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Detailed Solution

The oxidation states and the mpts are not related to the harness of the alloy. London dispersion forces are not significant factor in the nature of metallic bond and weaker inter particle forces would likely increase, not decrease the malleability. The smaller copper atoms prevent the movement of gold atoms in the alloy but being similar in size of silver and gold atoms crystal structure is not deformed and the atoms of the metals can slide easily.

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