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.
How is formalin useful?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Formalin is used as germicide, disinfectant and antiseptic
Formalin is the 40% aqueous solution of formaldehyde. Formaldehyde kills micro-organisms and hardens proteins, so formalin is used to preserve biological specimens and as a germicide, disinfectant and antiseptic.
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.”