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. ${Cu}_4{Ag}_{3}Au$
• D. $CuAgAu$

Answer 1

Answer: (C)

${Cu}_4{Ag}_{3}Au$

In the unit cell number of $Cu$ atoms $\left(fcc/ccp\right)$ $=8\times \frac{1}{8}+6\times \frac{1}{2}=4$

As $Ag$ atoms occupying edge centred $=12\times \frac{1}{4}=3$

and $Au$ atoms are presents at the body-centered $=1$

$\therefore$ Formula is ${Cu}_4{Ag}_{3}Au$.

Option C is correct.