JEE Main · 2017 · 02 Apr 2017 · Offline · Solid State

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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 :

(A)2a
(B) $22 a$
(C) $2 a$
(D) $\frac{a}{2}$ ✓ Correct

Answer: (D)

Solution

In a face-centred cubic lattice the atoms touch along the face diagonal, whose length

2 a

spans four radii:

4 r = 2 a

, so

r = \frac{a}{2 2}

. The closest approach is the centre-to-centre distance between neighbours,

2 r = \frac{a}{2}

JEE Main · 2017 · 02 Apr 2017 · Offline · Single correct option

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