Question

Which of the following exists as covalent crystals in the solid state?
a-Silicon
b-Sulphur
c-Phosphorous
d-iodine

Answer 1

Hint: Covalent crystals are those crystals which formed by sharing of valence electrons between two atoms. This results in the formation of a covalent bond between the atoms.

Complete step by step solution:
-A crystal or crystalline solid is a form of solid material. In this kind of solid, constituents are atoms, molecules or ions. They are arranged in a highly ordered microscopic structure to form a crystal lattice which extends in 3 Dimension structure.
Examples of crystal solid are salt, CsCl etc.
-A covalent network solid or network solid is a covalent solid. In this kind of solid, the atoms are bonded by covalent bonds in a continuous network throughout the material. In these solids, there are no individual molecules and the entire crystal or amorphous solid may be considered as a macromolecule. Formulas for such solids are same of those for compounds
Examples of covalent solids are diamond , silicon dioxide or quartz etc .
-Molecular solids are solids which are collections of molecules held together by weak intermolecular forces. These solid structures are maintained by intermolecular forces which are much weaker than strong bonds like metallic, covalent, or ionic bonds.
-Now let’s check the options provide:
-Silicon (Si): it is a covalent solid
-Sulphur () : it is a molecular solid
-Phosphorus (​) : it is also a molecular solid
-Iodine () : it is a molecular solid too.

Hence, the correct option is (A) Silicon.

Note: As the molecular solids consist of weak intermolecular forces, they are soft and easy to break. Sulphur , phosphorus and iodine come under this category and are soft and volatile.