Which two elements both have $4$ valence electrons and are commonly capable of forming long covalent chains in organic molecules?

• A. Oxygen and nitrogen
• B. Carbon and silicon
• C. Hydrogen and fluorine
• D. Sulfur and phosphorus

Answer: (B)

Verified step by step guidance

1. Identify the group in the periodic table that contains elements with 4 valence electrons. Elements in Group 14 (also called Group IV) have 4 valence electrons.
2. Recall that carbon (C) is a Group 14 element with 4 valence electrons and is well-known for forming long covalent chains, which is the basis of organic chemistry.
3. Recognize that silicon (Si), also in Group 14, has 4 valence electrons and can form long covalent chains similar to carbon, although less commonly in organic molecules.
4. Understand why other options are incorrect: oxygen and nitrogen have 6 and 5 valence electrons respectively; hydrogen and fluorine have 1 and 7 valence electrons; sulfur and phosphorus have 6 and 5 valence electrons.
5. Conclude that the two elements with 4 valence electrons capable of forming long covalent chains in organic molecules are carbon and silicon.