Question

Which of the following is a molecular solid?
A. Diamond
B. Graphite
C. Ice
D. Quartz

Answer 1

Hint: What are actually solids: Solid is a state of matter in which its constituent particles have fixed positions and can oscillate about their mean positions. Solids have definite shape, mass and volume. Have strong intermolecular forces and are rigid. Molecular solids are composed of molecules bounded by intermolecular forces. The crystal is held together by intermolecular forces not by bonds.

Complete answer:
There are two types of solids: one is crystalline and other is amorphous. Crystalline solids are further classified into four categories on the basis of nature of intermolecular forces which are molecular, ionic, metallic and covalent solids. Let us see the options to which category they belong.
- Diamond: Diamond is an allotrope of carbon with atoms arranged in crystal structure and has strong networked structure. The arrangement of atoms is extremely rigid in diamond. Diamond forms covalent bonds with its atoms due to which they are held very strongly at their positions. It is hard and brittle and has a high melting point. They are insulators and do not conduct electricity. Diamond and silicon carbide are examples of covalent solids.
-Graphite: It is soft and a good conductor of electricity. In graphite, carbon atoms are arranged in different layers and with each atom covalently bonded to three of its neighbouring atoms in the same layer. The fourth valence electron present between different layers is free. The free flowing electrons make graphite a good conductor of electricity. Different layers can slide one over the other which makes graphite a soft solid and a good solid lubricant. By forming covalent bonds, it comes under
- Ice: Ice is an example of Hydrogen Bonded Molecular Solids. Molecules of these solid forms polar covalent bonds between H and electronegative elements like \[\text{F ,O or N}\] atoms. Ice$\text{(}{{\text{H}}_{2}}\text{O)}$ is bounded by strong hydrogen bonding. It is a non-conductor of electricity. It is a volatile liquid or soft solid under room temperature.
- Quartz: Quartz is a strong substance because its molecules form network covalent structures. The structure forms a lattice-like structure. It is composed of oxygen and silicon atoms in silicon-oxygen tetrahedra ($\text{Si}{{\text{O}}_{4}}$). Each oxygen atom is shared between two tetrahedral atoms, making quartz as $\text{Si}{{\text{O}}_{2}}$. It is used to make oscillators for clocks and cell phones.

So, the correct answer is “Option C”.

Note: Any type of structure can be categorized to which solid it belongs by knowing the type of bond it forms. Like, Ionic solids have its constituent particles as ions which are bounded by electrostatic forces. Examples of Ionic solids are $\text{NaCl,MgO}$. This is how a structure can be categorized as which type of solid it is.