Which gas produces a red coloured light in a discharge tube? A.Mercury B.Argon C.Air D.Neon

To determine which gas produces a red-colored light in a discharge tube, let's analyze the options provided:

1. Mercury: When electrified, mercury primarily emits bluish light and has a characteristic spectrum that does not include red.

2. Argon: Argon typically produces a violet light when ionized, and it does not emit red light in a discharge tube.

3. Air: When air is excited in a discharge tube, it mainly emits a mixture of colors but not specifically red.

4. Neon: Neon gas is well-known for producing a bright red-orange light when subjected to a high voltage in a discharge tube.

Conclusion

Based on the analysis, the gas that produces a red-colored light in a discharge tube is D. Neon.