3 Replacement by fluoride ion: When arenediazonium chloride is
treated with fluoroboric acid, arene diazonium fluoroborate is
precipitated  which on heating decomposes to yield aryl fluoride 4 Replacement by H: Certain mild reducing agents like
hypophosphorous acid (phosphinic acid) or ethanol reduce
diazonium salts to arenes and themselves get oxidised to
phosphorous acid and ethanal, respectively