Question

When molten zinc is cooled to solid state, it assumes hcp structure. The number of nearest neighbours of the zinc atom will be?
(A) $4$
(B) $6$
(C) $8$
(D) $12$

Answer 1

Given that when molten zinc is cooled to solid state, it assumes a hexagonal close packing which can also be known as hcp structure. The unit cell in hcp structure is hexagonal and the number of nearest neighbors for an atom or coordination number in hexagonal close packing is $12$ .

Complete answer:
Some metals can be called as molten metals one of the examples is molten zinc which means the metal in liquid state. Molten zinc will be in liquid state and it takes the shape of the container. When liquids are cooled it undergoes freezing to form a solid metal.
Thus, molten zinc when cooled to solid state, assumes hcp structure. The smallest repeating unit in a crystal lattice is known as a unit cell. The unit cell in hcp structure is hexagonal. The number of atoms in hcp structure are $12$ in which there are six corner atoms in the top layer and six corner atoms in the bottom layer. The total neighbour atoms are $12$ which gives the coordination number of zinc atoms.

Note:
In hcp structure the spheres in alternate layers will lie on each other as it refers to the packing of closed spheres. Hexagonal close packing system is very common in the elements or metals like beryllium, magnesium, zinc, cadmium, titanium and zirconium.