While cooking, if the bottom of the vessel is getting blackened on the outside, it means that
  1. the food is not cooked completely.
  2. the fuel is not burning completely.
  3. the fuel is wet.
  4. the fuel is burning completely.

AcademicChemistryNCERTClass 10

Correct Answer: (b) the fuel is not burning completely.

Explanation: The unburnt particles of the fuel present in the smoke blacken the vessel from the outside.  This occurs due to incomplete combustion of fuel.

[Extra information: Combustion is actually a scientific term for burning. Combustion is a chemical process where any fuel has a reaction with air (oxidant) to produce heat energy.

it is given by :

Hydrocarbon + Oxygen → Carbon Dioxide + Water + Heat Energy

Types of Combustion are given below:-

1. Complete Combustion: One of the types of combustion is Complete Combustion. Complete combustion occurs in an unlimited supply of air, oxygen in particular.

Example: burning of a candle.

2. Incomplete Combustion: Incomplete combustion takes place when the air is in limited supply. It is dirt combustion, due to lack of oxygen, the fuel will not react completely, which in turn, produces carbon monoxide and soot instead of carbon dioxide.

Example: burning of paper.

Two disadvantages of incomplete combustion are given below:

  1. Due to incomplete combustion, a greater amount of fuel is wasted and less heat is released as compared to that in complete combustion.
  2. Incomplete combustion leads to the production of a gas called carbon monoxide which is extremely poisonous.]
Updated on 10-Oct-2022 12:47:17