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Sodium has body-centred packing. If the distance between two nearest atoms is 3.7 A, then lattice parameter is

Asked in CBSE AIPMT 1999 · Unit cells and lattice parameters

Answer: (1) 4.3 A

Step-by-step solution

Idea: in a body-centred cubic cell the closest pair is a corner atom and the body centre, which lie along the cube's body diagonal.

The body diagonal has length √3 a, and the nearest-neighbour distance is half of it: d=(√3 a)/2.

Rearranging: a=(2d)/(√3).

a=(2×3.7)/(1.732)=4.27 A, which rounds to 4.3 A.

Why the other options are wrong

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