Which of the following best explains why hydrogen and helium are the two most common elements in the universe?

• A. They are the only elements that can exist in the vacuum of space.
• B. They are constantly produced by radioactive decay of heavier elements.
• C. They were formed in large quantities during the Big Bang and are the simplest elements, making them more abundant.
• D. They are the only elements that do not react with other elements in stars.

Answer: (C)

Verified step by step guidance

1. Understand that the question is about the cosmic abundance of elements, specifically why hydrogen and helium are the most common in the universe.
2. Recall that the Big Bang theory explains the origin of the universe and the formation of the first elements shortly after it occurred.
3. Recognize that hydrogen and helium are the simplest elements, consisting of one and two protons respectively, which made them easier to form in the high-energy conditions of the early universe.
4. Note that heavier elements are formed later inside stars through nuclear fusion, so they are less abundant compared to hydrogen and helium.
5. Conclude that the best explanation is that hydrogen and helium were formed in large quantities during the Big Bang and their simplicity contributes to their abundance.