Which of the following gases will rekindle a brightly splint?

Analyze the question: The question (likely meant to say "a glowing splint") asks which gas relights a glowing wooden splint. This is the standard test for an oxidizing gas that supports combustion, usually oxygen.

Concept: A glowing splint is relit by oxygen. Some oxides of nitrogen also relight it because they decompose when heated and release oxygen:

• Nitrous oxide (N₂O) decomposes: 2N₂O → 2N₂ + O₂. The mixture is 1/3 oxygen, which is a higher proportion than in air, so it rekindles a glowing splint.
• Nitrogen dioxide (NO₂) is a brown gas that can support the combustion of strongly burning materials such as magnesium or burning phosphorus. It does not normally rekindle a glowing splint in the standard school test.
• Nitric oxide (NO) is the gas that does not relight a glowing splint at room temperature. It is rapidly oxidized to brown NO₂ in air.
• Chlorine (Cl₂) does not rekindle a splint. It bleaches damp litmus paper.

Step by step:

1. Identify the test: a glowing splint relighting indicates oxygen, or a gas that readily gives up oxygen.
2. Eliminate Cl₂ (D), since it bleaches litmus and does not release oxygen.
3. Eliminate NO (B), which is not a standard rekindler of a glowing splint.
4. Between NO₂ and N₂O, the textbook gas known to rekindle a glowing splint is N₂O (laughing gas), because it breaks down to give oxygen and nitrogen.

Answer: C.

Exam tip: Remember "N₂O relights, NO doesn't." Laughing gas (N₂O) is the oxide of nitrogen that behaves like oxygen in the glowing-splint test. NO₂ is recognized by its brown color and choking smell.