Question

In a binary compound, atoms of element A form a hcp structure and those of elements $M$ occupy $2/3$ of the tetrahedral voids of the hcp structure. The formula of the binary compound is:

• A. $M_{4}A$
• B. $M{A}_3$
• C. $M_2{A}_3$
• D. $M_4{A}_3$

Answer 1

The correct option is D $M_4{A}_3$

Number of atom in hcp unit cell = 6
So, $A=6$
Total number of tetrahedral void in hcp unit cell = 12
$\therefore M=\frac{2}{3}\times 12=8$

Thus, the formula of the binary compound would be $A_6{M}_8$
$A_3{M}_4$
$\text{or}{M}_4{A}_3$
Hence, option (b) is correct answer.