A solid is made of two elements X and Y. Atoms X are in fcc arrangement and Y atoms occupy all the octahedral sites and alternate tetrahedral sites. What is the formula of compound ?

Explanation

To determine the formula of the compound made of elements X and Y, we will follow these steps:

### Step 1: Determine the number of X atoms in the FCC arrangement
In a face-centered cubic (FCC) structure, the contribution of atoms can be calculated as follows:
- There are 8 corner atoms, each contributing \( \frac{1}{8} \) of an atom to the unit cell.
- There are 6 face-centered atoms, each contributing \( \frac{1}{2} \) of an atom to the unit cell.

Calculating the total number of X atoms:
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