What is the concentration of p

"concentration" means "amount of a particular substance in the sample".
in 1ml pure ethanol, as there's no impurities, there'll only be 1ml of ethanol present.
concentration = 1ml/1ml = 100%

pure = 100%, except in some rare cases:

ethanol absorbs water from air, and cannot be removed by simple distillation, so commercially-available "pure" ethanol has only about 96%.

concentrated sulfuric acid, normally has highest concentration of 98%, also due to same reason.
well, there're >100% sulfuric acid, but that's another story -- extra sulfur trioxide (SO3) is dissolved in conc. sulfuric acid, so it could go above 100%.

in trace-level analysis, nothing is pure. even the finest chemicals cannot be claim as 100%-pure, as there're ALWAYS trace amount of impurities. I'm doing such kind of analysis, so i know it quite well.


yet, Generally, we refer "pure" as 100%.