Question

A compound is formed by elements \(X\) and \(Y\). \(Y\) atoms make CCP and \(X\) atoms occupy all octahedral voids. What is the formula?

• A. \(X_2Y\)
• B. \(XY\)
• C. \(XY_2\)
• D. \(X_2Y_3\)

Hint:

In CCP or FCC structures: Octahedral voids = Number of atoms in the lattice. If all octahedral voids are filled, the ratio of void atoms to lattice atoms becomes \(1:1\).

Answer 1

The Correct Option is B

Concept: In a Close Packed Crystal (CCP) structure:
• If the number of atoms forming the close packing is \(N\),
• The number of octahedral voids present is also \(N\). If another atom occupies all octahedral voids, the ratio between the two types of atoms becomes directly comparable with the number of voids.

Step 1: Determine the number of atoms forming CCP. Let the number of \(Y\) atoms forming the CCP structure be: \[ N \]

Step 2: Determine the number of octahedral voids. In CCP: \[ \text{Number of octahedral voids} = N \]

Step 3: Determine the number of \(X\) atoms. Since \(X\) atoms occupy all octahedral voids: \[ X = N \] Thus, \[ X : Y = N : N \] \[ X : Y = 1 : 1 \]

Step 4: Write the chemical formula. \[ \boxed{XY} \]