The compound formed by elements P and Q has a cubic structure in which P atoms are at the corners of the cube and Q atoms are at the face centers. What is the formula of the compound?

As P atoms are at the 8 corners of the cube, ∴ Number of P atoms per unit cell =8×18=1 As Q atoms are at the face centres of the 6 faces of the cube,∴Number of Q atoms per unit cell =12×6=3∴Ratio of atomsP:Q=1 : 3Thus, the formula of the compound is PQ3.