In an fcc unit cell, atoms are numbered as shown below

The atoms not rouching each other are (Atom numbered `3` is face center of front face)

Options

A. `3 and 4`
B. `1 and 3`
C. `1 and 2`
D. `2 and 4`

Answer

c

Explanation

In fcc structure corner atoms do no touch each other (atom 1 and 2 ), but every face center atom touches corners .Moreovent atom previded it is not the opposite face center atom in an for unit cell
(i) Atoms 1 and 4 are louching each other where center to- cenrtered distance `= (6)/(sqrt(2)`
(ii) Atoms 1 and 2 are not touching each other
(iii) Atoms 2 and 4 are toughting each other center to - center distance`= (6)/(sqrt(2))`