Question

Which of the following exists as covalent crystals in Solid State?
(A) Sulphur
(B) Phosphorus
(C) Iodine
(D) Silicon

Answer 1

In this type of question, we are discussing the part of solid state (Solid state is the state of matter in which particles are closely packed and held by a strong intermolecular force of attraction) . They are classified into molecular , ionic metallic and covalent solids .

Complete step by step answer:
Covalent crystals are hard, frequently brittle materials such as diamond, silicon, and silicon carbide... In the simpler, monoatomic types, each atom is surrounded by a number of atoms equal to its valence.
A covalent network crystal consists of atoms at the lattice points of the crystal, with each atom being covalently bonded to its nearest neighbour atoms.
In covalent solids the constituent particles are atoms , and between them covalent bonding forces exist , they have a three - dimensional network . They are called giant molecules since a large number of atoms are present in one molecule . They are very hard and brittle and have a very high melting point and boiling point . Since they are composed of atoms and not ions they are insulators and do not conduct electricity. Through graphite is an exception as it is a soft and good conductor of electricity .
According to the Question,
Silicon: Covalent Solid
Sulphur: Molecular Solid
Phosphorus: Molecular Solid
Iodine: Molecular Solid

So, the correct answer is Option D .

Note:
Covalent bonds are extremely strong, so covalent solids are very hard. Generally covalent solids are insoluble due to the difficulty of solvating very large molecules. They are poor conductors of electricity since there are no delocalized electrons.