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# A cubic solid is made of two elements P and Q. Atoms of Q are at the corners of the cube and P at the body-centre. What is the formula of the compound? What are the coordination numbers of P and Q?

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.