What is the first element to form after the Big Bang?

• A. Helium
• B. Hydrogen
• C. Carbon
• D. Oxygen

Answer: (B)

In the early universe, as it cooled from an incredibly hot, dense state, light nuclei began to form in a process called Big Bang nucleosynthesis. The simplest and first available nucleus is a single proton, which is the nucleus of hydrogen. So hydrogen forms first because it’s the easiest, lightest building block—a lone proton. As cooling continues, more complex nuclei like deuterium and helium-4 appear, but hydrogen is the initial product and remains the most abundant. Heavier elements such as carbon and oxygen are mainly forged later inside stars. If you’re thinking in terms of atoms, neutral hydrogen atoms form later when electrons finally combine with protons during recombination.