Which one of the following causes pungency of mustard oil

Mustard seeds contain the substance Glucosinolate, also known as sinigrin. The crushing of mustard seeds for oil leads to the release of the enzyme myrosinase.
Thus the combination of myrosinase and Glucosinolate produces AITC (Allyl isothiocyanate), which is a wide-spectrum antimicrobial compound that is responsible for the characteristic pungency of mustard oil.