Which gas produces a red coloured light in a discharge tube?

Analysis

The question asks for the specific gas that emits a characteristic red-colored light when an electric discharge is passed through it in a vacuum or discharge tube.

Concept Explanation

When a high voltage is applied across a discharge tube containing a gas at low pressure, the gas atoms become excited. As these excited electrons return to their ground state, they release energy in the form of light (photons). The color of the light emitted is unique to the specific gas used because each element has a distinct energy level structure.

• Mercury vapor: Typically produces a bluish-green or ultraviolet light (often used in fluorescent lamps).
• Argon: Typically produces a pale lilac or violet light.
• Air: Produces a pale blue or white glow.
• Neon: Known for its distinct, brilliant reddish-orange glow, which is why it is widely used in "neon signs."

Step-by-Step Solution

1. Identify the phenomenon: This is an application of gas discharge physics, where different gases produce different emission spectra.
2. Evaluate the options: • Mercury (A) is used in vapor lamps for white/blue light. • Argon (B) is an inert gas that glows violet/lilac. • Air (C) contains a mixture of gases, resulting in a faint blue/white glow. • Neon (D) is a noble gas that emits a bright red-orange light when ionized in a discharge tube.
3. Conclusion: Based on the emission spectrum of noble gases, Neon is the correct gas that produces the red light.

Exam Tip

To remember this for your JAMB or WAEC exams, associate the word "Neon" directly with "Neon signs." If you have ever walked past a shop with bright red glowing signage, you are looking at the light produced by Neon gas!