What primarily composes the gases in nebulae?

Nebulae are primarily composed of hydrogen and helium, which together account for about 99% of the observable matter in these vast clouds of gas and dust in space. These two elements are the most abundant in the universe, formed in the early stages after the Big Bang.

Hydrogen, being the simplest and most plentiful element, serves as the primary building block for stars and galaxies, as it condenses under gravity to form new stars. Helium, formed from hydrogen through nuclear fusion processes within stars, also plays a crucial role in the lifecycle of stellar formations within nebulae.

The other choices present elements that, while they do exist in various cosmic structures, are not significant contributors to the overall composition of nebulae. For instance, oxygen and nitrogen are present in trace amounts and are more commonly associated with molecular clouds or specific stellar atmospheres rather than as the main components of nebulae. Similarly, carbon, sulfur, iron, and copper, while found in certain nebulae or related interstellar matter, make up a much smaller fraction compared to hydrogen and helium.