Which gas is commonly used to fill luminous advertising tubes (often called neon or tube lights) to produce a bright coloured glow?

Introduction / Context:
This general knowledge chemistry question asks about the gas used in glowing advertising tubes, often referred to as neon lights or tube lights. When a suitable gas is placed under low pressure in a sealed glass tube and an electric potential is applied, the gas can emit characteristic coloured light. Different gases give different colours, but the classic bright reddish orange glow is produced by neon gas, which is why such signs are commonly called neon signs.

Given Data / Assumptions:
- The context is luminous tubes used for signage and lighting.
- Options include oxygen, hydrogen, neon, and nitric oxide.
- We assume a typical low pressure gas discharge tube commonly used in advertising displays.

Concept / Approach:
Noble gases like neon, argon, and others emit characteristic colours when excited by electricity at low pressure. Neon, in particular, produces a bright orange red glow that is strongly associated with advertising signage. Oxygen and hydrogen are reactive diatomic gases that, under normal conditions, are not used alone to make stable luminous sign tubes. Nitric oxide is a reactive gas that is not appropriate for standard lighting applications. Therefore, among the options provided, neon is the gas most commonly used for neon sign tubes and is the correct answer.

Step-by-Step Solution:
Step 1: Recall that neon signs are named after the gas neon, which is used in many classic advertising tubes.
Step 2: Neon is a noble gas, chemically inert under most conditions, and safe to use in sealed glass tubes.
Step 3: When a high voltage is applied across the electrodes of a tube containing low pressure neon, electrons in neon atoms are excited and then fall back to lower energy levels, emitting light.
Step 4: The light emitted by excited neon atoms has a characteristic bright orange red colour, making neon ideal for visible signage.
Step 5: Oxygen and hydrogen do not produce such characteristic decorative glows in standard low pressure tubes and are not typically used for coloured advertising lights.
Step 6: Nitric oxide is a reactive gas and is not suitable for everyday lighting tubes.

Verification / Alternative check:
Practical observations of street signs and advertising boards show long glowing tubes that are commonly called neon signs. Reference material on lighting technology states that neon gas is used to produce the classic orange red emission, while other noble gases or phosphor coatings are used for different colours. Oxygen and hydrogen are mainly associated with combustion or industrial processes, not decorative discharge lamps. This confirms that neon is the standard gas used in such tubes.

Why Other Options Are Wrong:
- Oxygen: While essential for combustion and respiration, oxygen is not used on its own as a gas for colourful advertising tubes and would present safety concerns.

Why Other Options Are Wrong (continued):
- Hydrogen: Hydrogen is flammable and explosive in mixtures with air, making it unsuitable for common lighting tubes.
- Nitric oxide: This is a reactive nitrogen oxide gas with uses in medicine and industry but not in standard tube lighting for advertisements.

Common Pitfalls:
Sometimes learners confuse different types of tubes, such as fluorescent lamps, mercury vapour lamps, and neon signs. While fluorescent lamps use mercury vapour and phosphors, the classic narrow glass advertising tubes that glow orange red are usually filled with neon. Remember that the word neon in neon light refers directly to the gas neon, which helps avoid confusion with other lighting technologies.

Final Answer:
Neon is the gas commonly used in neon or tube lights for bright advertising displays.