Question

why do sometimes cooking vessels get blackened on gas or kerosene stove?​

Answer 1

Cooking vessels are kept on high inflammatory temperature on gas like methane,butane and kerosene .. Send nice cooking vessels are metals they leave residue when heated at such high temperature.

So they get blackened.

Answer 2

Let us look at the answer:

Explanation:

Cooking vessels sometimes get blackened due to incomplete combustion if the fuel.

LPG gas burns with a blue flame indicating the complete combustion of fuel. As it starts turning to yellow this implies incomplete combustion.

Kerosene stove also burns with completely blue flame.

Incomplete combustion blackens the surfaces of utensils as the unburnt gases deposits as carbon soot/black soot.