Which material is a giant covalent structure?

• A. Diamond
• B. Graphite
• C. Silicon dioxide
• D. Ammonia

Answer: (A)

A giant covalent structure is one where atoms are linked by covalent bonds throughout a continuous three-dimensional network. Diamond fits this perfectly: every carbon atom forms four strong covalent bonds to other carbons in a tetrahedral arrangement, creating an extended 3D lattice that goes on in all directions. This universal connectivity explains diamond’s extreme hardness and very high melting point.

Graphite, while covalently bonded, has layers where strong bonds exist within each layer but weaker forces hold the layers together; it doesn’t form the same uniform 3D network, so its properties differ (softer, conducts electricity along the planes). Ammonia consists of discrete molecules held together by intermolecular forces, not a network of covalent bonds. Silicon dioxide also forms a network solid, but the example most commonly highlighted as a classic giant covalent lattice among the options is diamond.