Question

$\text{C}{{\text{l}}^{\text{-}}}$ atom of the corner of its unit cell is equally shared by-----number of such unit cells.
(A) 4
(B) 8
(C) 6
(D) None of these

Answer 1

Hint: The unit cell of a crystalline solid is defined as the smallest repeating portion which shows the complete geometry of the crystalline substance. A unit cell is characterized by the edge length and angles in between the pair of edges. A unit cell contains eight corners, six faces, and one body centre.
Lattice points (ion, molecule or atom) in crystalline solid shows how the particles are arranged at different sites in crystalline solid.
There are seven types of crystal systems (Bravais lattice) and $\text{NaCl}$ shows a cubic type of crystalline system.

Complete Step by step solution:
In the cubic type of crystalline system a corner of a cube is common in eight cubes and each cube represents an individual unit cell. An atom present in the corner of the unit cell is shared by eight unit cells. So $\dfrac{\text{1}}{\text{8}}\text{th}$ part of an atom will be present at the corner of each unit cell.

Hence option (B) will be the correct answer.

Note: -A face of a cube (or unit cell) is common in two cubes, so $\dfrac{\text{1}}{2}\text{th}$ part of an atom will be present at the face of cube.
-An edge of a unit cell is common in four unit cells, so $\dfrac{\text{1}}{4}\text{th}$ part of the atom will present at the edge of a unit cell.
-A unit cell centre is not sheared in any other unit cell, so one complete atom will present at the unit cell centre.