International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

In a setup testing for oxygen, the presence of a glowing splint is a well-known indicator. When a glowing splint is introduced to a sample of oxygen, it will reignite, demonstrating that oxygen is present. This reaction occurs because oxygen supports combustion; thus, any smoldering material that is still hot enough can react with the oxygen and burst into flames.

The other options do not indicate the presence of oxygen clearly or are not relevant to such tests. A colored gas would suggest the presence of a different substance, rather than pure oxygen, while an odorless liquid does not offer any visual or interactive indication of oxygen. Similarly, a bubbling flask could indicate a chemical reaction or the release of a gas, but it alone does not confirm the presence of oxygen. In summary, the glowing splint serves as a definitive test for oxygen, making it the correct answer.