Pungency in onion is to due presence of

Pungency in onion is due to the presence of Allyl propyl disulphide.
Onion is valued for its bulbs having characteristic odour, flavour and pungency, which is due to the presence of a volatile oil allyl propyl disulphide.
Pungency is formed by an enzymatic reaction when tissues are broken. Bulbs are suited for storage for a long period and long-distance transport.