## Question

An alloy of Cu, Ag and Au is found to have Cu forming the simple cubic closed packed lattice. If the Ag atoms occupy the face centres and Au is present at the body centre, the formula of the alloy will be

### Solution

CuAg_{3} Au

Cu atoms are at eight corners of the cubic. Therefore, the number of Cu atoms in the unit cell = 8/8 = 1.

Ag atoms are at the face – centre of six faces. Therefore, its share in the unit cell = 6/2 = 3.

Au atoms are at the body centre,

∴ the number of Au atoms = 1

∴ The formula of the alloy is CuAg_{3} Au.

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