Question

In a FCC unit cell, atoms are numbered as shown below. The atoms not touching each other are: (Atom numbered $3$ is face centre of front face)

• A. $3\text{and}4$
• B. $1\text{and}3$
• C. $2\text{and 3}$
• D. $2\text{and}4$

Answer 1

The correct option is A $3\text{and}4$

Atoms not touching each other are two face centre atoms $3$ and $4$. Two neighbouring face centre and corner atoms will always touch other.