In living things, the source of the carbon-14 that is used in radiocarbon dating is carbon dioxide in the atmosphere.
Living things inhale oxygen, and exhale carbon dioxide into the atmosphere, which is why the air and atmosphere are so full of it.
<span>chemicals reacting are written on the left, what is formed is written on the right after the = sign
eg Copper + oxygen = copper oxide.
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The valence of helium is 0.