How is a pure substance different from a mixture? a: a pure substance is heterogeneous b: a mixture is made of one substance c: mixtures cannot be separated by physical means d: pure substances cannot be separted by physical means

the old alchemists made significant contributions to science even though there starting premises were off a bit. their conclusions after failure would steer them into better directions for investigation. science is no more than close observation and the initial mistakes result in rethinking and retrying experiments.