Question

How many unit cells are present in 39 gm of potassium that crystallises in body-centred cubic structure?

• A. $N_A$
  
• B. $\frac{N_A}{4}$
  
• C. $0.5N_A$
  
• D. $0.75N_A$

Answer 1

The correct option is C $0.5N_A$


No. of atoms =$\frac{39}{39}\times N_A=N_A$
In bcc unit cell = Z = 2
$\therefore$ No. of unit cell $=\frac{N_A}{2}=0.5N_A$