What a coincidence! Three days into National Chemistry Week, we dive further into STEM education to celebrate Mole Day. We’re not toasting the burrowing animal, but the unit of measurement (mole) used primarily in chemistry and molecular science studies. We don’t know how many moles of liquid nitrogen are in this photo, but we do like the dynamic look of the super-cooled element, which in liquid form can resemble boiling water. We hope this photo doesn’t depict liquid nitrogen after somebody in the lab dropped their keys into the vat. At minus 320 degrees Fahrenheit, liquid nitrogen tends to flash-freeze anything immersed in it.