Free Combustion and Flame 02 Practice Test - 8th Grade 

Question 1

Which of the following options can be correctly associated with fuels?

A.

Fuel is the substance that undergoes combustion.

B.

Fuel produces energy to be used for work.

C.

Fuel may be solid, liquid or gas.

D.

The substance which is highly infammable.

SOLUTION

Solution : A, B, and C

Fuel is defined as a substance that undergoes reaction with oxygen and produces energy. The process is called as combustion. The fuel can be liquid (kerosene), gas (methane) or solid (coal). The meaning of inflammable is that the substance has the ability to catch fire easily. Not all fuels are inflammable. Wood is one such example.

Question 2

What is the main chemical component present in striking surface of a matchbox?

A. Potassium
B. Phosphorus
C. Potassium chlorate
D. Graphite

SOLUTION

Solution : B

When a matchstick strikes on striking surface of a matchbox, the heat of the friction causes a reaction between the potassium chlorate in the match head and phosphorus in the striking surface.

Question 3

Every substance that burns produces flames.

A.

True

B.

False

SOLUTION

Solution : B

Substances produce flames while burning, only if it vapourises during the process.
For example, molten wax rises through the wick and is vapourised during burning. So, they form flames.
Charcoal, on the other hand, does not vaporise. So, it does not produce any flame.
Hence, the above statement is false.

Question 4

Which of the following is not a component of a fire triangle?

A. Oxygen
B. Nitrogen
C. Fuel
D. Heat

SOLUTION

Solution : B

A fire triangle is a simple model for understanding the necessary ingredients for production of fire. The triangle illustrates the three elements a fire needs to ignite: heat, fuel, and oxygen. Nitrogen gas does not support combustion. The image below shows a fire triangle.

Question 5

An ideal fuel is cheap, readily available, easily combustible and easy to transport. It has high calorific value. It does not produce gases or residues that pollute the environment.

Based on the above statements which of the following is closest to being an ideal fuel?

A.

Coal

B.

Petrol

C. Kerosene
D.

Compressed Natural Gas (CNG)

SOLUTION

Solution : D

There is probably no fuel that could be considered as an ideal fuel. We should look for a fuel which fulfils most of the requirements for a particular use. Compressed Natural Gas (CNG) contains methane which doesn't produce a large amount of toxic gases or residue that pollute the environment. It is also easily combustible. Of the given options it is closest to being an ideal fuel.

Question 6

You may have seen that when a person accidentally catches fire, people put a blanket around him. Identify the reason for this.

A.

The material of the blanket stops fire.

B.

The blanket is non-combustible.

C.

The blanket cuts off the supply of oxygen which in turn stops combustion.

D.

 The blanket reduces burning.

SOLUTION

Solution : C

The essential requirements for producing fire are fuel, air (to supply oxygen), and heat. Fire can be controlled by removing one or more of these requirements.

As oxygen gas is essential for combustion, we can stop the fire by cutting the supply of oxygen. This can be done by wrapping a blanket around the person. So, it stops the combustion and the person can be saved.

Question 7

Which of the following oxides upon dissolving with rain cause acid rain?

A. Nitrogen dioxide
B. Sulphur dioxide
C. Silicon dioxide
D. Sodium oxide

SOLUTION

Solution : A and B

Motor vehicles and the industries located in and around Agra releases sulphur dioxide and nitrogen dioxide into the atmosphere. These gases dissolve in rain water and form acids like sulphuric acid and nitric acid. These acids fall to the ground in form of rain and this rain is called acid rain.

Question 8

What is the unburnt material that is present in a fuel, e.g. wood?

A. Ash
B. Coal
C. Coke
D. Carbon

SOLUTION

Solution : A

Ash is the solid residue of a fuel. It is the material that is left unburnt at the end of combustion. Its chemical composition does not contain carbon.

Question 9

The efficiency of a fuel is expressed in terms of its ________.

A. calorific value
B. density
C. purity
D. volume

SOLUTION

Solution : A

Fuel efficiency is expressed in terms of calorific value and its unit is kilojoule per kg. It is the amount of heat produced on complete combustion of 1kg of a fuel.

Question 10

Whenever there is a flame, smoke will surely be produced.

A.

True

B.

False

SOLUTION

Solution : B

Smoke and flame are produced due to different reasons.

A flame is produced when the gases released when a fuel is burnt are combustible. These gases then catch fire which we see as a flame.

Smoke is a result of partial combustion or some leftover unburnt particles. These tiny, unburnt particles get released into the air alongwith the gases of combustion and get mixed with the air which we see as smoke.

These two things can happen independently and thus occurence of one event does not guarantee the occurence of other.