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1. A candle is mainly a source of light and heat. 

2. A candle is made of wax in which a thick thread inserted wax in the candle melts when it is lighted by a match stick. 

3. A little of wax forms vapour. 

4. This vapour combines with oxygen in the air to form flame. 

5. The heat of the flame melts more of the wax from the top of the candle. 

6. The melted liquid wax moves upward through the thread. It also changes to vapour when it reaches the top of the wick and byrns with the flame.

The products formed are carbondioxide and water because wax is mixture of hydrocarbons.

Combustible materials: The materials which burn when brought near a flame are called combustible materials, 

e.g. : Petrol, diesel, kerosene, etc. 

Non-combustible materials: The materials which do not burn when brought near a flame are called noncombustible materials, 

e.g.: Pebbles, sand, clay, iron, etc.

1. Sand 

2. Clay 

3. Iron 

4. Steel

1. Petrol 

2. Diesel 

3. Kerosene 

4. Alcohol

Burning material in the presence of air (oxygen) is called combustion.

Oxygen or air is needed for combustion to take place.

The mass of fuel = 4.5 kg 

The heat produced = 1,80,000 KJ heat produced 1,80,000 

The calorific value of fuel =

\(\cfrac{heat \,produced}{mass \,of \,the \,fuel}\) = \(\cfrac{1,80,000}{4.5}\) = 40,000 KJ/Kg

mass of the fuel 4.5

A) Necessity of air for burning

The substances which burn in the air are called combustible.

No, moon reflects entire sunlight that falls on the surface because it acts as perfect reflector. Whereas earth is also acts as reflector but green house gases

present in atmosphere absorbing the sunlight and resending on earth. So paper can be burnt on earth by using magnifying glass but it is not possible on moon.

a) The cup which does not have water.

b) The water in the second cup is hot because the heat received by second cup is transferred to water in it. The water in this cup prevents the paper to reach its ignition temperature and hence it does not burn.

c) When it reaches its ignition temperature.

A) 1 – b, 2 – c, 3 – e, 4 – a, 5 – d

Correct option is B) LPG

If we put a burning match stick into the container having oxygen it burns with bright flame the reason is oxygen supports combustion.

Correct option is  C) Potassium permanganate

Rusting of Iron is a combustion reaction. Combustion is a process in which elements combine with oxygen. During formation of rust iron atoms combine oxygen in the air forming iron oxides or rust.

A) 1 – c, 2 – d, 3 – b, 4 – e, 5 – a

Correct option is D) sand

Correct option is C) alcohol

Correct option is A) Oxygen

Correct option is  C) Oxygen

Ways adopted by fire fighters: 

1. The fire fighters immediately put off the electric mains and start spraying water on the fire. The water spray cool the combustible material below the ignition tempera¬ture. This prevents fire from spreading. Then the heat turns the water into vapours which surround the burning material and prevent supply of oxygen to the burning material. So the fire extinguishes. 

2. For electrical fire accidents or fire accidents involving oil and petrol water is not useful. So fire fighters use carbondioxide. It is heavier than oxygen and does not affect the electric equipment.

Correct option is B) Ignition

No, combustion is not possible without oxygen because it is a reaction of material with oxygen that is an oxidation process. For example, carbon compounds react with oxygen and form carbon-dioxide and water. So no combustion reaction is possible without oxygen.

Phosphorous is highly reactive with air containing oxygen. It has low ignition temperature. So it catches fire at room temperature. So it is preserved in water.

Correct option is D) Iron

Calorific value of a fuel is the amount of heat energy produced on complete combustion of 1 kg of that fuel. It is measured in kilo joules per kg. (kJ/kg)

In the second situation water will get heated in a short time in the outermost part in the flame complete combustion takes place so which is hottest part whereas yellow part is in the middle zone of candle where partial combustion takes place and it is moderately hot.

Spontaneous combustion is observed in burning of match stick. When the match stick is struck against the rubbing surface the red phosphorous converts into white phosphorous which immediately react with potassium chlorate in the match stick head to produce enough heat to ignite antimony sulphide and start the combustion.

Rapid combustion is observed in gas stoves. When we turn the nob of the gas stove in the kitchen and bringing a burning match stick near to it. The gas burns rapidly and produce heat and light.

We can put off a fire by covering with sand or blanket because we are preventing supply of oxygen. So we can say oxygen is needed for burning.

Correct option is D) Petrol, Diesel

I feel that fuels are essential part of human life in their day to day life. Starting from the morning before they going to sleep they would found application of fuels. In the morning for breakfast we need fuel for cooking. For seeing TV or working with computer we need fuel because they run by electricity from thermal power (coal). If we want to go to school or office we use vehicle which required fuel. Every electrical articles like fans, mixies works by taking electricity from coal. So we conclude that fuels are essential part of human life.

Correct option is  D) All the above

Remedies to avoid air pollution:

1. Look for alternative sources of energy like wind energy, solar energy, tidal energy which does not produce pollution. 

2. Try to minimise the use of fuels that is for travelling short distances use bicycles and try to go by bus (public transport) for offices which will minimise the use of fuels and there by air pollution. 

3. Ensure regular maintenance of vehicle and engine which will release the less quantity of harmful gases there by decrease of air pollution.

4. Use CNG (compressed natural gas) as fuel as it is less pollutant and release small quantity of harmful gases.

The stick starts burning with flame because oxygen supports combustion.

Correct option is  B) LPG

No, different fuels produce different amount of heat when they are burnt.

A candle is made of wax in which a thick thread is inserted. When it is lighted melts by a match stick. A little of the wax forms gas. This gas combines with oxygen in the air to form flame. But coal is a natural fuel contains more carbon. When it is burnt it sends out carbon monoxide and carbon dioxide gases and becomes ember and does not emit a flame. Coal is the changed material of wood. Hence it does not emit a flame as it possesses a huge calorific value (heat).

Correct option is B) Harini

We need oxygen to burn a material.

Except a small rock and a pebble, the rest of them are burnt.

Burning is a process of reaction of a material with oxygen. The materials which have weak molecular bonds easily react with oxygen so they burn easily. The material which have strong molecular bonds does not react with oxygen easily because the molecular bonds should be broken before they react with oxygen.

The water spray cools the combustible material so that its temperature decreases. This prevents the fire from spreading.

Water is not used to control fires involving electric equipments because water is good conductor of electricity (water having dissolved salts) so it may conduct electricity and harm those trying to douse the fire.

Wax in the candle melts when it is lighted by a match and a little wax forms vapour. This vapour combines with oxygen in the air to form flame. The heat of the flame melts more of the wax from the top of the candle. The melted liquid wax move upward through the thread. It also changes to vapour when it reaches the top the wick and burns w’ h the flame. Wick is not required in gas burners because LPG has low ignition temperature so it is easily convert into vapour state.

We can put off the fire by using the fire extinguishers in which CO₂ gas is present.

Combustion takes place only in the presence of oxygen. When we cover a burning object with sand or blanket that would cut off the supply of oxygen to burning object. So the fire is puts off.

1. Put off the electric mains. 

2. Do not pour water on fires caused by electricity water containing dissolves salts is a good conductor of electricity. 

3. Do not pour water on fires due to petrol and oil because water is more denser the u oil and petrol.

B) Use fire extinguisher