Question

Cruciferous plants, when crushed, emit a pungent smell due to the presence of
A. Oxalic acid
B. Alkaloids
C. Iron compounds
D. Sulphur compounds

Answer 1

Cruciferous plants are the plants of the family Brassicaceae which is also known as Cruciferae, with many genera, species, and cultivars that are being raised for food production. It includes vegetables such as cauliflower, cabbage, kale, garden cress, bok choy, broccoli, Brussels sprouts, and similar green leaf vegetables. The cruciferous vegetables are rich in nutrients which include several carotenoids, vitamins C, E, and K, folate and minerals. In addition to this, the cruciferous vegetables also contain a group of substances that are known as glucosinolates, which are sulfur containing chemicals.

Complete answer:
Oxalic acid: An organic compound found in many plants is oxalic acid. Leafy greens, vegetables, fruits, cocoa, nuts and seeds do contain oxalic acid. Human body can produce oxalate on its own or can obtain it from food. Vitamin C, when metabolized, can be converted into oxalate. The pungent smell of cruciferous plants is not due to oxalic acid.
Hence option A is not correct.
Alkaloids: A class of basic, naturally occurring organic compounds that contains at least one nitrogen atom are known as alkaloids. Some related compounds with neutral and even weakly acidic properties are included in this. Alkaloids do not cause pungent smell in cruciferous plants.
Hence option B is not correct.
Iron compounds: An essential micronutrient for almost all living organisms is the iron. Iron required for the synthesis of chlorophyll in plants and the maintenance of chloroplast structure and function. They do not cause a pungent smell.
Hence option C is not correct.
Sulphur compounds: A primary source of dietary sulfur are the cruciferous vegetables. They provide sulphur in a form known as glucosinolates. These are chemicals which are responsible for the pungent smell and bitter flavor of cruciferous vegetables. The glucosinolates in cruciferous vegetables are broken down during food preparation, chewing, and digestion. So, cruciferous plants emit a pungent smell when they are crushed.
Hence option D is the correct answer.

Hence, Option D. Sulphur compounds are the correct answer.

Note:
Glucosinolates are present in cruciferous vegetables which are under research for their potential to affect cancer. Glucosinolates are hydrolyzed to Isothiocyanates or ITCs with the help of myrosinase. Isothiocyanates are currently investigated for their chemopreventive and chemotherapeutic effects. Finding that the ITC phenethyl isothiocyanate reduced levels of the oncoprotein $MCL1$ is an example of this.