Question

At very low temperature, oxygen $({O_2})$ freezes and forms a crystalline solid. Which term best describes the solid?
A.Covalent network
B.Molecular crystals
C.Metallic
D.Ionic

Answer 1

In crystalline solids components are structured in a highly ordered microscopic arrangement, such as electrons, molecules or ions, forming a lattice of crystals that stretches in all directions. Molecules are held together by van der Waals forces in crystals. We have to analyze each crystalline solids in order to understand the type of this solid mentioned in the question.

Complete step by step answer:
Let us look through the characteristics of all types of all the types of given crystals.
Covalent crystals are hard and have very melt on high temperatures, that is, they possess high melting points. This is because the attractions are very strong between covalently bonded atoms. About conductivity, they do not conduct electricity because the electrons are bound too tightly to the bonds with the elements.
Let us now look about metallic crystals. They are generally malleable, ductile, sonorous, shiny and are very good conductors of both electricity and heat. They are bounded by metallic bonds, the chemical bonds in which mobile electrons are shared over many nuclei. This leads to electrical conduction among the crystals.
Ionic crystals are very hard, have rocketing melting points and boiling points, but are brittle. When they melt, the liquids which are formed as a product of melting those crystals conduct electricity very well. These behaviours reflect the very strong attractive forces between ions of opposite charge as well as the repulsions that occur when ions of like charge are placed near each other.

Molecular crystals are solid forms of crystals in which the lattice sites are occupied either by atoms - as in solid Argon or Krypton - or by molecules - as in solid $CO_2, SO_2, or H_2O$. Such crystals tend to be soft and have low melting points because the particles in the solid experience relatively weak intermolecular attractions.
Now let us compare Oxygen with the crystals. Oxygen naturally occurs as a molecule. It is not formed by ionic bonds or covalent bonds and it is a non-metal. Hence all these points prove that the crystal that is formed when Oxygen is frozen should be a molecular crystal.
Hence the correct answer is Option B- Molecular Crystals.

Note:
Based on the different characteristics of the given solids, any type of question can be asked. They can be either asked on physical properties like appearance, color, melting points, boiling points, electrical conductivity and thermal conductivity and the arrangement of atoms in the crystal and their lattices. Examine and find out the type of the given compound, since the type of bonds is bounded so that it decides what crystal it forms.