Answer:-

• A face-centred cubic (fcc) unit cell has particles at the eight corners plus particles at the centre of its six faces.
• Each particle present at the corner of a given unit cell is shared with seven other neighbouring unit cells. As a result, its contribution to the given unit cell is only 1/8.
  Thus, the number of particles present at corners per unit cell
  = 8 corner atoms x 1/8 atom per unit cell = 1
• Each particle at the centre of the six faces is shared with one neighbouring cube. Thus, 1/2 of each face particle belongs to the given unit cell.
  Thus, the number of particles present at faces per unit cell
  = 6 atoms at the faces x 1/2 atom per unit cell = 3
  Therefore, fcc unit cell has one corner particle plus 3 face particles, making total of 4 particles per unit cell.