A compound is formed by two elements P and Q. The element Q forms ccp and atoms of element P occupy half of tetrahedral voids. What is the formula of the compound?

$PQ$

The correct answer is Option (1) → $PQ$.

To determine the formula of the compound, we can analyze the arrangement of atoms and the type of voids occupied in the crystal structure.

Element Q forms a cubic close-packed (ccp) structure: In a ccp structure, the number of Q atoms per unit cell is 4 (because there are 4 atoms in a ccp unit cell).

Element P occupies half of the tetrahedral voids: In a ccp structure, the number of tetrahedral voids is 2 times the number of atoms in the unit cell. Since there are 4 atoms of Q, there will be 8 tetrahedral voids.

Since P atoms occupy half of the tetrahedral voids, the number of P atoms per unit cell will be half of 8, which equals 4 tetrahedral voids.

Q atoms (ccp structure): 4 atoms per unit cell.

P atoms (half of the tetrahedral voids): 4 atoms per unit cell.

Thus, the ratio of P to Q is 4:4, or simplified as 1:1.

Since the ratio of P to Q is 1:1, the formula of the compound is PQ.