NCERT Exemplar solutions for Science [English] Class 8 chapter 6 - Combustion and Flame [Latest edition]

A substance which reacts with oxygen giving heat is called a combustible substance. Which one of the following is a combustible substance?

Which one of the following has the highest calorific value?

Magnesium ribbon on burning in air produces

Which of the following is not a combustible substance?

The substance that does not burn with flame is

On placing an inverted tumbler over a burning candle, the flame extinguishes after some time. This is because of non-availability of

If a person’s clothes catch fire, the best way to extinguish the fire is to

The substance expected to have the highest ignition temperature out of the following is

Choose the correct statement about inflammable substances from the following.

They have

Choose the incorrect statement from the following.

Forest fires are usually due to

The calorific value of a fuel is expressed in a unit called

In villages, people use wood as fuel because

Which one among the following is considered as the cleanest fuel?

Choose the incorrect statement from the following.

A good fuel is one which

Shyam was cooking potato curry on a chulha. To his surprise, he observed that the copper vessel was getting blackened from outside. It may be due to –

A ______ process in which a substance reacts with ______ to give off heat is called combustion.

When the clothes of a person catch ______ the person is covered with a ______ to extinguish fire. 

The ______ temperature at which a substance catches fire is called its ______ temperature.

 The substances which gave very ______ ignition temperature and can easily catch fire with a flame are called ______ substances.

The substances which vaporise during ______ give flame.

Some words (underlined) in the following sentence is jumbled up. Write them in their correct form.

Seldie is a combustible substance.

Some words (underlined) in the following sentence is jumbled up. Write them in their correct form.

Slaags is a non-combustible material.

Some words (underlined) in the following sentence is jumbled up. Write them in their correct form.

Chittsmack does not burn by itself. 

Some words (underlined) in the following sentence is jumbled up. Write them in their correct form.

Some substances on combustion produce thea and mafel.

Some words (underlined) in the following sentence is jumbled up. Write them in their correct form.

The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its ficalroic value. 

Two glass jars A and B are filled with carbon dioxide and oxygen gases respectively. In each jar, a lighted candle is placed simultaneously. In which jar, will the candle remain lighted for a longer time and why?

Anu wants to boil water quickly in a test tube. On observing the different zones of the flame, she is not able to decide which zone of the flame will be best for boiling water quickly. Help her in this activity.

Why is the use of diesel and petrol as fuels in automobiles being replaced by Compressed Natural Gas (CNG) in big cities?

Boojho wants to separate the following materials as combustible and non-combustible. Can you help him? 

State whether the following statement is True/False.

Air is necessary for combustion.

State whether the following statement is True/False.

Magnesium is a non-combustible metal.

State whether the following statement is True/False.

Carbon dioxide is an excellent fire extinguisher.

State whether the following statement is True/False.

Calorific value of wood is higher than that of coal.

Match the items of Column A with the items of Column B.

Match the following for the flame of a candle.

If you hold a piece of iron wire with a pair of tongs inside a candle flame or a Bunsen burner flame, what will you observe? Will it produce a flame?

Fill in the blanks using the words given in the box.

 A chemical process in which a substance reacts with oxygen to give off heat is called ______.

Fill in the blanks using the word given in the box.

 Wood, paper, CNG are ______ substances.

Fill in the blanks using the word given in the box.

The lowest temperature at which a substance catches fire is called its ______ temperature.

Fill in the blanks using the words given in the box.

Ignition temperature of ______ is lower than that of wood.

Fill in the blanks using the words given in the box.

The substances which have very low ______ temperature and can easily catch fire with a flame are called ______ substances.

Fill in the blanks using the words given in the box.

The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its ______.

People usually keep angithi/burning coal in their closed rooms during winter season. Why is it advised to keep the door open?

Write True/False against the following statement and also correct the false statement.

A physical process in which a substance reacts with oxygen to give off heat is called combustion.

Write True/False against the following statement and also correct the false statement.

Water is the best extinguisher for fires involving electrical equipment.

Write True/False against the following statement and also correct the false statement.

Alcohol, CNG and LPG are inflammable substances.

Write True/False against the following statement and also correct the false statement.

Increased concentration of nitrogen in air is believed to cause global warming.

Write True/False against the following statement and also correct the false statement.

Greater the calorific value, better is the fuel.

Write True/False against the following statement and also correct the false statement.

Middle zone is the hottest zone of a flame.

Write True/False against the following statement and also correct the false statement.

The substances which vaporise during burning, give flame.

Cracker on ignition produces sound. Why?

You are provided with three watch glasses containing milk, petrol and mustard oil respectively. Suppose you bring a burning candle near these materials one by one, which material(s) will catch fire instantly and why?

Manu was heating oil to fry potato chips. The cooking oil all of a sudden caught fire, he poured water to extinguish the fire. Do you think, this action was suitable? If yes, why? If not, why not? In such a condition what should Manu have done?

What are the three essential requirements to produce fire? How fire extinguisher is useful for controlling the fire?

Give two examples each for a solid, liquid and gaseous fuel along with some important uses.

The calorific values of petrol and CNG are 45000 kJ/kg and 50, 000 kJ/kg respectively. If you have vehicle which can run on petrol as well as CNG, which fuel will you prefer and why?

Although wood has a very high calorific value, we still discourage its use as a fuel. Explain.

Forest fire produces a lot of air pollution. Write in brief about the reasons of forest fires.

Complete the crossword with the help of the clues.

Across

1. Non-metal which catches fire if exposed to air. (10)

3. The lowest temperature at which a substance catches fire is called its ______ temperature. (8)

5. The most common fire extinguisher. (5)

Down

2. A chemical process in which a substance reacts with oxygen to give off heat. (10)

4. Petrol is used as a ______ in automobiles. (4) 

6. It is as hard as stone and black in colour. (4)