An example of covalent solid is

CONCEPT:

Covalent Solids

• Covalent solids, also known as network solids, are solids where atoms are bonded together by covalent bonds in a continuous network extending throughout the material.
• They have high melting points and are usually very hard. Examples include diamond, silicon carbide, and quartz.

EXPLANATION:

• Let's examine the given options:
  • Option 1: MgO
    • Magnesium oxide (MgO) is an ionic solid, not a covalent solid. It consists of Mg²⁺ and O^2- ions held together by ionic bonds.
  • Option 2: Mg
    • Magnesium (Mg) is a metallic solid, where atoms are held together by metallic bonds.
  • Option 3: SiC
    • Silicon carbide (SiC) is a covalent solid. In SiC, each silicon atom is covalently bonded to four carbon atoms, forming a very hard and high-melting-point network.
  • Option 4: CaF₂
    • Calcium fluoride (CaF₂) is an ionic solid, consisting of Ca²⁺ and F^- ions held together by ionic bonds.

Therefore, the correct answer is option 3: SiC.