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Copper has face centered cubic (fcc) lattice with interatomic spacing equal to 2.54 A. The value of lattice constant for this lattice is

Asked in CBSE AIPMT 2005 · Unit cells and lattice parameters

• (1) 2.54 A
• (2) 3.59 A
• (3) 1.27 A
• (4) 5.08 A

Step-by-step solution

Why the other options are wrong

• (1) 2.54 A is the interatomic spacing copied straight across; the lattice constant is the cube edge, which is longer by √2.
• (3) 1.27 A halves the spacing to get the atomic radius, which is a different quantity again.
• (4) 5.08 A doubles the spacing, as though nearest neighbours sat a full cube edge apart.

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