Shyam was cooking potato curry on a chulha. To his surprise, he observed that the copper vessel was getting blackened from outside. It may be due to:
Correct answer - (c): improper combustion of the fuel.
Improper combustion of fuel produces undesirable substances and also a lot of black smoke due to incomplete combustion.
The copper vessel was getting blackened from outside due to improper combustion of the fuel.