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In chemistry, a reactivity series is an calculated, and structurally analytical progression of a series of metals, arranged by their "reactivity" from highest to lowest. It is used to summarize information about the reactions of metals with acids and water, double displacement reactions and the extraction of metals from their ores. (Wikipedia)
Some of the lessons taught in a chemistry class in Pripyat, i sure the experiments in this school where explosive, as i'm sure H&S wasn't heard of in those days. On my visit I could see that there was some chemical bottles still scattered throughout the classroom and storage room, most where empty, but a few still had powder of some chemicals still within.