All fossil fuels are in limited quantity. Thus we need a very judicious use of these fuels. For this, we must find out some alternative sources of energy as solar energy, water energy, geothermal energy etc. We must ask them to reduce unnecessary use of vehicles e.g., if four people are going from one place to single destination, they should use only one vehicle rather than more than one.

These days the head of the match sticks contains only antimony trisulphide and potassium chlorate. The rubbing surface has powdered glass and a little red phosphorus. When the match stick is struck against the rubbing surface i.e., some red phosphorus, this immediately reacts with potassium chlorate on the match stick head to produce enough heat to ignite antimony trisulphide and start combustion.

Types of combustion: It is of three types:
(i) Rapid combustion: When gases burn rapidly to produce heat and light, it is called rapid combustion.
(ii) Spontaneous combustion: When material suddenly bursts into flame, without the application of any apparent cause, it is called spontaneous combustion.
(iii) Explosion: When combustion takes place with sudden release of heat, sound, light and gas with a bang it is called explosion.

To show that air is necessary for burning a candle.
Experiment:
(i) Fix a lighted candle on a table.
(ii) Put a glass chimney over the candle in such a way that air can enter the chimney. We find that candle burns freely.
(iii) Now, fix a glass chimney in a way that no air enters in the glass.
(iv) The flame flickers and produces smoke.
(v) The flame finally goes off because the air is not available. It is already used by the candle to burn
So, this concludes that air is necessary for burning a candle.

(i) The name of two energy sources that we would consider to be exhaustible are coal and petroleum.
(ii) They will be exhaustible when continuously extracted. Moreover, the formation of these fuels under the earth takes a longer period of time.

A matchstick does not catch fire on its own at room temperature because the ignition temperature of matchstick is much higher than the room temperature. The matchstick starts burning on rubbing it on the rough side provided on the matchbox. It is because the heat produced by friction heats the chemical at the head of the matchstick to its ignition temperature and makes it burn.

A matchstick can burn a splinter of wood directly because it has low ignition temperature, whereas a matchstick cannot burn a log of wood directly as it has high ignition temperature. In order to burn a log of wood, a small fire is first started by burning straw (or dry grass), or paper by a matchstick, then the log of wood is placed over this fire. This fire heats the log of wood to its ignition temperature due to which it starts burning.

If fire is due to oil, then water is not suitable fire extinguisher because it is heavier than oil and settles down below the oil. In such cases, sand or soil should be used.
They cut off the supply of air to the fire. Thus, fire can be controlled.

The watch glass containing petrol will catch 'lire Instantly because its ignition temperature is very low. Also petrol is an inflammable substance, i.e. it can easily catch fire with a flame.

The water heated by Ramesh will get heated in a shorter time because he kept his beaker near the hottest (non-luminous) zone of the flame.

The process of rusting cannot be called combustion because in this process, no heat and light is produced. Due to this reason, iron is not considered as combustible substance.

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.

Calorific value of a fuel is expressed in kilojoule per kilogram (kJ/kg).

(a) Water is not used to control fires involving electrical equipments because water is a good conductor of electricity. So, it can easily conduct electric current and causes danger of electric shocks.
(b) LPG is a better domestic fuel than wood because LPG has more calorific value and produces no pollution. While wood produces smoke and causes more pollution.
(c) It is because the ignition temperature of paper is less, so it catches fire easily. It does not catch fire, when wrapped around aluminium pipe because aluminium absorbs the heat by conduction, so paper does not attain its ignition temperature

Difference between LPG and wood are as follows: