Outermost Zone: It is blue coloured part because complete combustion takes place in this part due to sufficient amount of oxygen. It is the hottest part of the flame.
Middle Zone: The colour of the middle zone is yellow because incomplete combustion takes place in this part due to the lack of oxygen. It is less hot than other part of the flame.

Carbon dioxide (CO₂) is the best fire extinguisher. Being heavier than oxygen, it covers the fire like a blanket. Since, the contact between the fuel and oxygen is cut-off, the fire is controlled. It also brings down the temperature of the fuel. That is why, it is an excellent fire extinguisher.

When the clothes of a person catch fire the person is covered with a blanket to extinguish fire because blanket cuts off the supply of air, that is the supporter of fire.

No, all the substances do not catch fire at the same temperature. Different substances need different temperature to catch fire.

Carbon monoxide gas is formed as a result of incomplete combustion.

The harmful effects of burning fuels:
(i) Fuels like wood, coal, petroleum etc. which are carbon fuels, produce unburnt carbon particles, which cause respiratory diseases (asthma) and skin diseases.
(ii) Generally CO₂ is released during burning of fuels. It causes the rise in the temperature of the atmosphere of earth, which is called global warming.
(iii)Incomplete combustion of fuel releases many poisonous gases such as carbon monoxide. It can kill people sleeping in a room by causing suffocation.
(iv) Combustion of coal and diesel generates sulphur dioxide. It can kill people sleeping in a room by causing suffocation.
(v) Burning of fuels releases oxides of nitrogen and sulphur. They dissolve in rain water and form acid. Such rain is called acid rain. It is harmful to crops, buildings and soil.

Three essential requirements to produce fire are as follows:
(i) Fuel
(ii) Air and
(iii) Heat to acquire the ignition temperature. The job of fire extinguisher is to cut off the supply of air or to bring down the temperature of fuel or both. The most common fire extinguisher is water. But water works only when things like wood and paper are on fire. For fires involving electrical equipment and inflammable materials like petrol, carbon dioxide (C0₂) is the best extinguisher. CO₂ being heavier than oxygen, covers the fire like a blanket. Since, the contact between the fuel and oxygen is cut-off, so the fire can be controlled. The added advantage of CO₂ is that in most cases, it does not harm the electrical equipment.