What gas emits light when an electrical current passes through it?

• A. Argon
• B. Neon
• C. Krypton
• D. Xenon

Answer: (B)

Neon is the correct answer because it is a noble gas that, when subjected to an electrical current, emits a distinct reddish-orange glow. This phenomenon occurs due to the excitation of neon atoms. When the electrical current passes through the gas, it energizes the electrons, causing them to jump to a higher energy level. As these electrons return to their original state, they release energy in the form of light.

This property has led to neon being widely used in neon signs and lighting applications. Other noble gases, like argon, krypton, and xenon, can also emit light when electrified, but they produce different colors and are less commonly associated with visible light applications compared to neon. For instance, argon typically emits a pale blue light. Thus, while other gases can emit light, the characteristic glow of neon is particularly recognized and is what distinguishes it in this context.