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Books, Other scientist's research, the Internet.
Using the pH=-log[ hydrogen ions], assuming the pH of water is 7 then using the concept that kw=[ OH] [H+], then the [H+]= 10 power minus 7,since kw=10 to the power minus 14
Since each of the substances conduct electricity except A, it is the least likely to be metallic. Additionally, it is a powder, which is unlike most metals, and has an extremely high melting point much above many metal substances and very different from the other substances tested.