Mustard pungency is due to:
That points to C: Glucosinolate breakdown. Compared with the other options, Glucosinolate breakdown is the one that correctly describes the PLANT SEC METABOLITES concept. The wrong ones are A) Alkaloids; B) Phenolics; D) Terpenes. If you’re stuck, eliminate anything that contradicts a basic fact you already know for this topic.
Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.