Ga (atomic mass 70 u) crystallizes in a hexagonal close packed structure. The total number of voids in 0.581 g of Ga is __________ $$\times$$ 10²¹. (Round off to the Nearest Integer). [Given : N_A = 6.023 $$\times$$ 10₂₃]

A certain element crystallises in a bcc lattice of unit cell edge length 27$$\mathop A\limits^o $$. If the same element under the same conditions crystallises in the fcc lattice, the edge length of the unit cel in $$\mathop A\limits^o $$ will be ____________. (Round off to the Nearest Integer).

[Assume each lattice point has a single atom]

[Assume $$\sqrt 3 $$ = 1.73, $$\sqrt 2 $$ = 1.41]

The number of octahedral voids per lattice site in a lattice is _________. (Rounded off to the nearest integer)

The unit cell of copper corresponds to a face centered cube of edge length 3.596 $$\mathop A\limits^o $$ with one copper atom at each lattice point. The calculated density of copper in kg/m³ is ___________. [Molar mass of Cu : 63.54 g; Avogadro Number = 6.022 $$\times$$ 10²³]