Chemical X is a mysterious formula owned by Professor Utonium.
Stored in an Erlenmeyer flask that has a piece of paper with an "X" taped to it, Chemical X is a purple liquid.
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While being stored on a shelf in the basement lab of the Utonium home, the chemical is stolen by Old Man Withers at the same time Professor Utonium is kidnapped. A note is left on a shelf, where it is usually stored, for the Powerpuff Girls to find, sparking an investigation by both Mystery Inc. and the girls. It is later discovered, tied up beside Professor Utonium, in the Mayor's office at Townsville Hall. It is presumed to have been reacquired by Professor Utonium following the capture of Old Man Withers.