The Solid State

The Solid State

Question

A metal crystallises in a face centred cubic structure. If the edge length of its unit cell is'a', the closest approach between two atoms in metallic crystal will be

  • 2a

  • 2 square root of 2 straight a
  • square root of 2 straight a end root
  • fraction numerator straight a over denominator square root of 2 end fraction

Answer

D.

fraction numerator straight a over denominator square root of 2 end fraction

In FCC unit cell atoms are in constant along face diagonal
So, √2a = 4R
therefore, the closest distance
left parenthesis 2 straight R right parenthesis space equals space fraction numerator square root of 2 straight a over denominator 2 end fraction space equals space fraction numerator straight a over denominator square root of 2 end fraction

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