# 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.

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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?

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The atom at the corner makes $\frac{1}{8}$ contribution while atom at body centre makes 1 contribution to the unit cell.

No. of atoms of Q per unit cell = 8 × $\frac{1}{8}$ = 1

No. of atoms of P per unit cell = 1 × 1 = 1

Therefore, formula of the compound is PQ.

The atom at the body centre would be in contact with all the atoms at the corners. Hence, the coordination number of P is 8.

Similarly, the coordination number of Q is 8 because it is shared by 8 other atoms.