Chemical X gives the Powerpuff Girls their superpowers in the original series.
Professor Utonium creates Blossom, Bubbles, and Buttercup while attempting to make the perfect little girl from sugar, spice, and everything nice. Chemical X is accidentally added to the mixture, triggering their creation and granting them extraordinary abilities.
The girls’ powers include flight, super strength, speed, durability, and energy-based attacks. The accidental ingredient is therefore central to the show’s origin story, not merely a later explanation for their abilities.
Chemical X is sometimes confused with Compound Z, which belongs to other Powerpuff Girls continuity and adaptations. For the original English-language series, the canonical term is Chemical X.