Question

In an ionic crystalline solid, atoms of element Y forms hcp structure. The atoms of element X occupy one third of tetrahedral voids. What is the formula of compound?

• A. $X_2Y_3$
• B. $XY$
• C. $X_3Y_3$
• D. $XY_2$

Hint:

Chemistry Tip: In close packing, tetrahedral voids = $2n$ and octahedral voids = $n$.

Answer 1

The Correct Option is A

Step 1: Let number of Y atoms $=n$ in hcp arrangement.

Step 2: Number of tetrahedral voids in close packing: $$ =2n $$

Step 3: X occupies one-third of tetrahedral voids. $$ X=\frac{1}{3}(2n)=\frac{2n}{3} $$

Step 4: Ratio of X:Y $$ \frac{2n}{3}:n=2:3 $$

Step 5: Empirical formula: $$ X_2Y_3 $$ $$ \therefore \text{Correct option is (A).} $$