Final answer:
Hydrogen and helium, elements with an atomic number less than lithium, were formed during the Big Bang, not through nuclear fission or during the birth of new stars. Therefore, the correct answer is b. Formed during the Big Bang.
Step-by-step explanation:
Elements with an atomic number less than lithium, such as hydrogen and helium, formed during the Big Bang. The Big Bang theory states that the universe started as a singularity, undergoing rapid expansion, which resulted in the formation of hydrogen and helium within the first few minutes, along with a small quantity of lithium, through nuclear reactions.
Following the Big Bang, the universe cooled down, ending the period of cosmic fusion where helium could form, making it so that no elements beyond lithium were produced during this time.
The heavier elements that we find on Earth were formed later, through nuclear fusion in stars, and not through the process of nuclear fission or during the birth of a new star from a nebula.
According to the Big Bang theory, the universe started with an explosive expansion about 12-15 billion years ago, and during the first few minutes, hydrogen, helium, and a small amount of lithium were formed through nuclear reactions. However, elements with atomic numbers greater than lithium formed through nuclear fusion in stars.