# Free Combustion and Flame 03 Practice Test - 8th Grade

If ignition temperature of a substance is lower than room temperature then it will undergo spontaneous combustion.

A. True
B. False

#### SOLUTION

Solution : A

A certain minimum temperature is required to initiate combustion reaction. This temperature is called ignition temperature.
A type of combustion where an external agent is not required and the material catches fire automatically is called spontaneous combustion. When the ignition temperature is lesser than the room temperature, combustion takes places on its own without the application of any external agent.

The middle zone of a candle flame is also called the zone of ______ combustion.

A.

complete

B.

partial

C. rapid
D.

spontaneous

#### SOLUTION

Solution : B

In the middle zone of candle flame, incomplete combustion takes place.

Air has to be blown around coal for it's easy combustion.

A.

True

B.

False

#### SOLUTION

Solution : A

If air is blown around coal, then air circulation increases the supply of oxygen gas which will help in the complete combustion of coal. Supply of sufficient amount of oxygen gas lets the coal burn completely.

When sufficient oxygen is not available, combustion of methane produces ______ gas and water.

A.

carbon dioxide

B.

carbon monoxide

C.

hydrogen

D.

nitrogen

#### SOLUTION

Solution : B

Incomplete combustion takes place when sufficient amount of oxygen is not present. Incomplete combustion of fuels containing carbon like wood, coal, methane, petroleum, etc releases carbon monoxide (CO) gas which is a very poisonous gas.

Calorific value is expressed in a unit called kilojoule per kg (kJ/kg).

A.

True

B.

False

#### SOLUTION

Solution : A

The calorific value of a fuel is expressed in a unit called kilojoule per kg (kJ/kg). Calorific value is the term that is used to measure the efficiency of a fuel.

Select the options that are needed for a matchstick to burn.

A. Friction
B. Chemical
C. Wood
D. Oxygen

#### SOLUTION

Solution : A, B, C, and D

The three essential things that are required for a substance to burn are heat, fuel and oxygen.
Here the heat is produced by friction between matchstick and box. Fuel is the chemical at the strip of matchstick and wood. Oxygen is available in the atmosphere.

Water works as a fire extinguisher by removing

A.

only heat

B.

only oxygen

C.

heat and oxygen

D.

the source of combustible substance.

#### SOLUTION

Solution : C

Water removes heat and cuts off the supply of oxygen when it is used as a fire extinguisher.
Water cools the combustible material so that its temperature is brought below its ignition temperature. This prevents the fire from spreading. Water vapours also surround the combustible material, helping in cutting off the supply of air so that the fire is exhausted. But water cannot be used for fires involving electrical equipment and inflammable substances.

Water cannot be used to extinguish ________.

A. household fires
B. electrical fires
C. forest fires
D. burning paper

#### SOLUTION

Solution : B

Water is a good fire extinguisher. But, water cannot be used to extinguish electrical fires. This is because water is a good conductor of electricity. It can cause electric shock and can harm the person who is trying to put it off.

When a cracker is ignited, a sudden reaction takes place with the evolution of heat, light and sound. Identify the type of combustion?

A. Explosion
B. Spontaneous combustion
C. Random combustion
D. Rapid combustion

#### SOLUTION

Solution : A

When a cracker is ignited, a sudden reaction takes place with the evolution of heat, light and sound. A large amount of gas liberated during this reaction. Such a reaction is called explosion.

The combustion reaction which occurs on its own, without any external supply of heat is called as:

A. Rapid combustion
B. Spontaneous combustion
C. Explosion
D. Fire

#### SOLUTION

Solution : B

The type of combustion in which a material suddenly bursts into flames, without any external heat supply is called spontaneous combustion. For example, substances like phosphorus and sodium burn when kept open at room temperature.