Question

Shyam was cooking potato curry on a chulha. To his surprise he observed that the copper vessel was getting blackened from outside. why?

Answer 1

the copper vessel become blackened because when the stove is not burning it get oxidized and form green coating but when you burn the rust on copper react with CO2 thus form blackened

Answer 2

The copper vessel was blackened from outside because of insufficiency of oxygen. When there is insufficient oxygen is provided, then the vessels get blackened from outside.