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What is the simplest formula of a solid whose cubic unit cell has the atom A at each corner, the atom B at each face centre and a C atom at the body centre?

Answer»

Solution :An ATOM at the corner of a cube is SHARED among 8 unit cells. As there are 8 corners in a cube, NUMBER of corner atom (A) per unit cell `=8 xx 1/8=1`
A face-centred atom in a cube is shared by two unit cells. As there are 6 faces in a cube, number of face-centred atoms (B) per unit cell =` 6 xx 1/2=3`
An atom in the body of the cube is not shared by other cells.
`therefore`number of atoms (C) at the body CENTRE per unit cell = 1. Hence the formula of the solid is `AB_3C`.


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