The test for this is fairly simple.
We take a glowing match or splint near the gas sample, if the glow intensifies, oxygen is present.
If a lit splint or match goes out with a popping sound, this means that hydrogen is present.
Answer:
Pro exercise con suffication
Explanation:
...
<span> the atmosphere holds about 21 per cent oxygen. Over the Earth’s 4.6 billion year history, oxygen did not appear in the atmosphere until perhaps about 2.5 billion years ago. Since then, oxygen levels have fluctuated in tandem with global geological and biological events, such as mass extinctions.</span>
