Astronomy Practice Exam 2025 – Complete Preparation Guide

The correct answer is based on the understanding of cosmic nucleosynthesis that occurred shortly after the Big Bang. The primary elements that emerged during this critical period of the universe's formation were hydrogen and helium.

During the first few minutes following the Big Bang, the universe was extremely hot and dense, allowing for nuclear reactions to occur. Protons and neutrons began to form, leading to the synthesis of hydrogen (the simplest and most abundant element in the universe) and helium (the second lightest element). These two elements combined make up about 98% of the ordinary matter in the universe today.

While other elements such as carbon and oxygen were formed later in the interiors of stars through stellar nucleosynthesis and supernova explosions, and elements like nitrogen and argon have also emerged from similar processes, they were not created directly during the Big Bang phase. Instead, they were synthesized much later in the life cycle of stars. Therefore, when discussing the fundamental elements that originated from the Big Bang itself, hydrogen and helium are the primary products that are universally acknowledged in cosmology.