Final answer:
The most widely used concentration of formalin, an aqueous solution of formaldehyde, is about 37% formaldehyde by weight. Formalin is used for various purposes including preserving tissue specimens and embalming bodies.
Step-by-step explanation:
Formaldehyde is sold as an aqueous solution called formalin, which contains about 37% formaldehyde by weight. This concentration range is the most widely used in various applications. Formalin is used for preserving tissue specimens, embalming bodies, and sterilizing soil or other materials. It is also used in the production of plastics and electrical resistance materials such as Bakelite.