Why is $\mathrm{carbon}$ present in so many types of molecules?

• A. Because $\mathrm{carbon}$ atoms are always found as free atoms and do not bond with other elements.
• B. Because $\mathrm{carbon}$ can form $4$ covalent bonds, allowing it to create a wide variety of stable structures such as chains, rings, and branches.
• C. Because $\mathrm{carbon}$ can only form ionic bonds, which are common in organic molecules.
• D. Because $\mathrm{carbon}$ is the most electronegative element, making it highly reactive with all other elements.

Answer: (B)

Verified step by step guidance

1. Understand that carbon's versatility in forming molecules is due to its ability to form covalent bonds rather than existing as free atoms or forming ionic bonds.
2. Recall that carbon has four valence electrons, which allows it to form up to four covalent bonds with other atoms, enabling a variety of bonding patterns.
3. Recognize that this tetravalency allows carbon to bond with other carbon atoms and different elements, creating diverse structures such as chains, rings, and branches.
4. Appreciate that these stable covalent bonds lead to the vast diversity of organic molecules found in nature and synthetic compounds.
5. Note that carbon is not the most electronegative element, so its bonding behavior is more about sharing electrons covalently rather than high reactivity or ionic bonding.