Which one of the following acids is secreted by leaves of Nettle that causes painful stings ?

The stinging hairs of nettle leaves (Urtica dioica) inject methanoic acid into the skin upon contact, which causes a burning sensation and painful stings [2]. Methanoic acid is also commonly known as formic acid [3]. While historical beliefs primarily attributed the irritation to formic acid, modern research indicates that the stinging fluid is a complex cocktail containing other substances such as histamine, acetylcholine, and serotonin, which contribute to the inflammatory response and skin reactions like urticaria. However, in the context of standard chemical classifications for natural sources, methanoic acid is the primary acid identified with nettle stings [2]. Other options like citric acid (found in lemons), tartaric acid (found in tamarind), and acetic acid (found in vinegar) are not the secretions responsible for the nettle's sting [2].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Self defence by animals and plants through chemical warfare > p. 27
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Table 2.3 Some naturally occurring acids > p. 28
3. [3] Science-Class VII . NCERT(Revised ed 2025) > Chapter 2: Exploring Substances: Acidic, Basic, and Neutral > 2.3 Neutralisation in Daily Life > p. 18