As atoms of Q are present at the 8 corners of the cube.Number of atoms of Q in the unit cell $=\large\frac{1}{8}$$\times 8=1$

As atoms P are present at the body centre,therefore number of atoms of P in the unit cell =1

$\therefore$ Ratio of atoms = P : Q=1 : 1

Hence,the formula of the compound is PQ.Atoms at the body-centre would be in contact with all the atoms at the corners.Hence,the coordination number of P would 8,similarly,coordination number of Q is also 8.