Question

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

• A. M₂A₃
• B. MA₃
• C. M₄A
• D. M₄A₃

Answer 1

The correct option is D

M₄A₃

Solution:

• For a hexagonal close packing (HCP) the total number of tetrahedral voids per unit cell is 12.
• The total number of spheres in HCP is 6.
• Therefore, the number of tetrahedral voids is double the number of spheres.
• As A → hcp and M → 2/3^rd of tetrahedral
• M_{2 × 12/3} A₆ = M₈A₆ = M₄A₃

So, the correct answer is option D.

Options (A),(B) and (C) don't satisfy the relationship between HCP and the number of tetrahedral voids (M_{2 × 12/3} A₆).