Which element is responsible for the most prominent deep red color in most emission nebulae?

Answer

Hydrogen

The most prominent color, deep red, almost always signals the presence of energized hydrogen gas, which is the most abundant element and whose characteristic H$ ext{H} ext{ extalpha}$ transition emits visible light around 656.3 nanometers.

Which element is responsible for the most prominent deep red color in most emission nebulae?
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