Which of the following is a sweet smelling substance?

Esters

The correct answer is option 3. Esters.

Esters are organic compounds characterized by a sweet, fruity smell. They are commonly found in various fruits and flowers, contributing to their pleasant aroma. Esters are formed through the reaction between an alcohol and a carboxylic acid, resulting in the elimination of a water molecule.

Esters have a specific chemical structure consisting of a carbonyl group (>C=O) bonded to an oxygen atom, which is further bonded to an alkyl or aryl group (R). The R group on the ester molecule determines its specific odor. For example, methyl ethanoate \((CH_3COOCH_3)\), commonly known as methyl acetate, has a fruity smell resembling apples.

Esters are naturally occurring compounds found in various fruits, flowers, and other plant materials. They are responsible for the characteristic sweet and fruity aroma of many fruits, such as bananas, strawberries, and pineapples, as well as the pleasant scents of flowers like roses and jasmine.

Due to their pleasant aroma, esters are widely used in the fragrance and flavor industry to impart sweet, fruity, and floral notes to perfumes, cosmetics, food products, and beverages. They are also used as solvents and as flavoring agents in various food and beverage products.

In summary, esters are sweet-smelling substances due to their chemical structure, presence in nature, low molecular weight, and widespread use in fragrances and flavors. They contribute to the delightful aromas of fruits, flowers, and many consumer products.