**Question:**

A compound is formed by two elements M and N. The element N forms *ccp *and atoms of M occupy 1/3rd of tetrahedral voids. What is the formula of the compound?

**Solution:**

The *ccp* lattice is formed by the atoms of the element N.

Here, the number of tetrahedral voids generated is equal to twice the number of atoms of the element N.

According to the question, the atoms of element $M$ occupy $\frac{1}{3}$ rd of the tetrahedral voids.

Therefore, the number of atoms of $M$ is equal to $2 \times \frac{1}{3}=\frac{2}{3}$ rd of the number of atoms of $\mathrm{N}$.

Therefore, ratio of the number of atoms of $M$ to that of $N$ is $M: N=\frac{2}{3}: 1$

$=2: 3$

Thus, the formula of the compound is M2 N3.

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