The answer is A, biogeochemical cycles.
The correct answer of the given question above would be option D. None of the above. When a solid has a low melting point, it is most likely a simple molecular substance. When it is ionic, covalent or metallic, it is already considered as a solid with a high melting point.
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This allows us to tell alkenes apart from alkanes using a simple chemical test. Bromine water is an orange solution of bromine. It becomes colourless when it is shaken with an alkene. Alkenes can decolourise bromine water, but alkanes cannot.
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