Steam from boiling is vapor. It consists of single H2O molecules floating in air. Theres a lot and they start clumping together quickly to form the mist you see.
The mist from a humidifier is tiny drops of liquid water thrown into the air mechanically. each drop has millions of water molecules. If it’s tap water there’s also thousands of calcium and chlorine atoms. If it’s stale water ther may also be a bacterium in there.
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