What is formalin, the chemical that killed a 3-year-old cancer patient at AIIMS Bhopal?

A 3-year-old blood cancer patient died at AIIMS Bhopal after being administered formalin through an IV line. Formalin is a solution made by dissolving formaldehyde gas in water. Its primary purpose is preservation. When doctors remove tissue during biopsy, the sample is often placed in container filled with formalin. Formalin is also used to preserve organs, biological specimens and cadavers.