Question

when why cut onions why do we cry

Answer 1

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.

Answer 2

When you cut open an onion a gas called Propanethiol S-oxide is realised and when the Propanethiol is mixed with enzymes it creates a sulphur gas, when the gases reaches your eyes it irritates them causing you to cry.