Question

why we get tears when we chop onions?

Answer 1

When you chop onions, a gas is released known as Propanethiol S-oxide. When it mixes with certain enzymes in the onion, it creates sulphur gas. When these acids gets into our eyes, it irritates our eyes. So eyes produce tears to protect itself...
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Answer 2

Lachrymatory-factor synthase is released into the air when we cut an onion. The synthase enzyme converts the amino acids sulfoxides of the onion into sulfenic acid. The unstable sulfenic acid rearranges itself into syn-ropanethial-S-oxide. Syn-propanethial-S-oxide gets into the air and comes in contact with our eyes.