Number of atoms in close packing = 0.5 mol

1 mol has 6.022x10²³ particles

So that

Number of close- packed particles = 0.5 × 6.022 × 10²³ = 3.011 × 10²³

Number of tetrahedral voids = 2 × number of atoms in close packing plug the value we get

Number of tetrahedral voids = 2 × 3.011 × 10 ²³ = 6.022 × 10 ²³

Number of octahedral = number of atoms in close packing

So that

Number of octahedral voids = 3.011 × 10 ²³

Total number of voids = tetrahedral voids + octahedral voids

= 6.022 × 10 ²³ + 3.011 × 10 ²³

= 9.03 × 10 ²³