Question

An alloy of copper, silver and gold is found to have copper atom constituting the ccp lattice. If silver atom occupy the edge centres and gold atom is present at body centred, the alloy has a formula

• A. $Cu_{4}Ag_{2}Au$
• B. $Cu_{4}Ag_{4}Au$
• C. $Cu4_{A}g_{3}Au$
• D. $CuAgAu$

Answer 1

Answer: (C)

$Cu4_{A}g_{3}Au$

Answer 2

In the unit cell number of Cu atoms (fcc/ccp)
$= 8 \times \frac{1}{6} + 6 \times \frac{1}{4} = 4$
As Ag atoms occupying edge centred
$=12 \times \frac{1}{4} = 3$
and Au atoms are presents at the body centred = 1
$\therefore$ formula, $Cu_4 Ag_3Au$