Formaldehyde is the first member of the aldehyde series. It is present in green leaves of plants where its presence is supposed to be due to the reaction of \(CO_2\) with water in the presence of sunlight and chlorophyll. Commercially, formaldehyde is obtained by the controlled oxidation of methane in the presence of molybdenum oxide \((MoO)\) acting as a catalyst. Formaldehyde is a constituent of a number of polymers also called resins. These are non volatile solids or semi solids which are obtained directly from certain plants and can be synthesized in the laboratory.
What is formalin?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Formalin is \(40\%\) aqueous solution of formaldehyde.
Formaldehyde is a gas at room temperature. It is very soluble in water, and its 40% aqueous solution is called formalin. This solution is used to preserve biological specimens and to prepare bakelite and urea–formaldehyde glues.
NCERT (2026-27 edition):
Uses of Aldehydes and Ketones – “… Formaldehyde is well known as formalin (40%) solution used to preserve biological specimens and to prepare bakelite (a phenol-formaldehyde resin), urea-formaldehyde glues and other polymeric products.”