Which second period element is classified as a covalent network solid in its standard state?

• A. Carbon
• B. Phosphorous
• C. Oxygen
• D. Iodine

Answer: (A)

Carbon is classified as a covalent network solid in its standard state, particularly in the form of diamond. In a covalent network solid, atoms are bonded by covalent bonds in a continuous network extending throughout the material. This results in very high melting and boiling points, as well as significant durability.

In the case of carbon, the diamond structure features each carbon atom bonded to four other carbon atoms in a three-dimensional tetrahedral arrangement, creating an extremely strong and rigid lattice. This network structure is the reason why diamond is one of the hardest known materials.

The other elements listed do not exhibit a covalent network solid structure in their standard states. Phosphorus typically exists as P4 molecules, forming molecular solids rather than networks. Oxygen exists as O2, a diatomic molecule, and iodine is found as I2, also a molecular solid with weak Van der Waals forces between the molecules. None of these forms a continuous network similar to that of diamond in carbon.