onion is used much more than in the world including pakistan. It is used in burger, also used as a salad while eaten cooked food at home.Onions where they are used to prepare food at homes, they also force them to tear during cutting.
On this occasion, this question often take place in mind that what is the reason , why it force the cutter to cry?
This question was so important that the US Congress Library's web page has been answering why cutting onion makes tear in eyes.
The short ANSWER is "non stable chemicals" DETAILED ANSWER is Two chemicals present in onion these are syn-propanethial-S-oxide and lachrymatory-factor synthase due to these tears come out.
The second chemical is then removed in the air when we cut the onions. This is an amino acid present on the chemical onions, which changes the sulfur oxide into cellular oxide. Shortly this acid itself re-convert itself into syn-propanethial -S- The shape of the oxide takes shape and forces the eye to stimulate the gland or the tears.
@abishali