A student collects the gas given off by pondweed in bright light, by displacement of water, for 10 minutes. A glowing splint put into the gas does not relight.
Which is the most likely explanation?
The gas has too low a proportion of oxygen, as other gases are collected too
Pondweed gives off carbon dioxide rather than oxygen when it is in bright light
The test needs a lit splint, because a glowing splint cannot detect oxygen gas
The oxygen reacted with the water, so none of it reached the collecting tube
97 exam-style questions on Edexcel GCSE Chemistry 9.2 Earth and atmospheric science, covering 9.2.1 The Earth's early atmosphere, 9.2.2 How the atmosphere evolved, 9.2.3 Chemical test for oxygen, and 9.2.4 The greenhouse effect and climate change. Each one has a worked solution and a mark scheme showing where the marks go.