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Substances and objects - class-VIII

Description: substances and objects
Number of Questions: 18
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Tags: insects and human welfare economic importance of plants and animals earth to sky let's regain our fields chemistry biology changes around us substances in daily use evs introduction to biotechnology changes around us food production animals in daily life what if it finishes?
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All chemical reactions are :

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. reversible

  2. irreversible

  3. exothermic

  4. endothermic

Show answer
Correct Option: B
Explanation:

A change in which one or more than one new substances are formed is known as a chemical change. 


A chemical change is also called a chemical reaction. Chemical reactions are not reversible.

Hence the option B is correct.

Sheet erosion is due to _________.

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. fast running rivers

  2. heavy rains

  3. occasional rains

  4. wind

Show answer
Correct Option: B
Explanation:

Sheet erosion is the detachment of soil particles by raindrop impact and their removal downslope by water flowing overland as a sheet instead of in a definite channel.


Hence, the correct option is $\text{B}$

Which of the following changes are irreversible?

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. Milk to paneer

  2. Cow dung to biogas

  3. Grain to its flour

  4. All of the above

Show answer
Correct Option: D
Explanation:

All of the following changes are irreversible because we can not convert the product into reactant again.
1) Milk to paneer.
2) Cow dung to biogas.
3) Grain to its flour.

 Iron adopts changes slowly and gradually by process of :

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. rusting

  2. moldings

  3. fermentation

  4. explosions

Show answer
Correct Option: A
Explanation:
Iron adopt changes slowly and gradually when it comes in contact with air (moisture, oxygen etc)
When Iron reacts with $'n'$ molecules of water in the pressure of oxygen, it forms rust. Hence the process is known as a rusting.
$4Fe+3{ O } _{ 2 }+2n{ H } _{ 2 }O\longrightarrow 2{ Fe } _{ 2 }{ O } _{ 3 }.n{ H } _{ 2 }O$

 Burnt sparklers and burnt books pages are examples of 

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. reversible change

  2. irreversible change

  3. no change

  4. none of the above

Show answer
Correct Option: B
Explanation:

Burnt sparklers and burnt books pages are examples of irreversible changes, as they are permanent changes which cannot be undone. Once these materials are burnt in to ashes, the original materials cannot be recovered back.

Which of the following is not a reversible change?

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. Heating of water to steam

  2. Cooking of egg to scrambled eggs

  3. Heating of wax to molten wax

  4. Cooling a cake

Show answer
Correct Option: B

Which of the following change cannot be reversed ?

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. Hardening of cement

  2. Freezing of ice cream

  3. Opening a door

  4. Melting of choclate

Show answer
Correct Option: A
Explanation:

A reversible change is a physical change that can be undone. 
A final substance can be converted back to the original substance without creating any new material.
An irreversible change is a permanent change that cannot be undone.


A. Hardening of cement is an irreversible change as we cannot reverse back to the original cement powder form once the cement hardens.
B. Freezing of ice-cream is reversible change as it can be reversed back by heating and it will convert to original form.
C. Opening of a door is reversible change as it can be reversed simply by closing the door 
D. Melting of chocolate is reversible change as it can be reversed by cooling the chocolate to its original form.
Option A is the correct answer.

Burnt sparklers and burnt books pages are examples of:

chemistry changes around us can all changes be reversed? substances and objects classification of changes

  1. reversible process

  2. irreversible process

  3. rusting

  4. none of these

Show answer
Correct Option: B
Explanation:

Irreversible changes $-$ because when they are burnt formation of gas and ashes takes place i.e. chemical reaction is taking place and new substance are formed which can't be reversed back.


      Book pages  $\quad \xrightarrow { \text{burning} } \quad { CO } _{ 2 }+$ other substances.

Hence, the correct option is $\text{B}$

Which of the following fiber is used to make wireless receiver?

biology substances in daily use can all changes be reversed? substances and objects changes around us

  1. Cotton fiber

  2. Silk fiber

  3. Wool

  4. Nylon

Show answer
Correct Option: B
Explanation:
The silk fiber is used to make a wireless receiver. fiber optic receivers capture the light from a fiber optic cable, decode the binary data it is sending and then convert into an electrical signal.

Which of the following is characterized by the fine soft under hair?

biology substances in daily use can all changes be reversed? substances and objects changes around us

  1. Yak

  2. Goat

  3. Sheep

  4. All of the above

Show answer
Correct Option: C

Angora wool is obtained from____________.

biology substances in daily use can all changes be reversed? substances and objects changes around us

  1. Worm

  2. Yak

  3. Goat

  4. Sheep

Show answer
Correct Option: C
Explanation:
Angora wool is obtained from Goat. 
The fleece taken from an Angora Goat is called Mohair. A goat produces four to five kg of hair per year.

Which of the following fiber was first developed in the China?

biology substances in daily use can all changes be reversed? substances and objects changes around us

  1. Wool

  2. Silk

  3. Cotton

  4. None of the above

Show answer
Correct Option: B

The most fibre are chemically composed of non-starch polysaccharides.

biology substances in daily use can all changes be reversed? substances and objects changes around us

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

The most fibre are chemically composed of non-starch polysaccharides like cellulose, inulin, lignin, chitins, pectins, oligosaccharides. They are either obtained from plants or animals. They are either soluble or insoluble. 

Which of the following is called as queen of fibers?

biology substances in daily use can all changes be reversed? substances and objects changes around us

  1. Angora wool

  2. Pashmina

  3. Silk

  4. Nylon

Show answer
Correct Option: C
Explanation:
Silk is called a queen of fibers. Because it is of good quality and it thus makes it expensive too.

Human life require which kind of material for leaving?

evs substances in daily use can all changes be reversed? substances and objects changes around us

  1. Food

  2. Fuel

  3. Home

  4. All of these

Show answer
Correct Option: D
Explanation:
Food is something that provides nutrients. 

Nutrients are substances that provide: energy for activity, growth, and all functions of the body such as breathing, digesting food, and keeping warm; materials for the growth and repair of the body, and for keeping the immune system healthy.

Fossil fuels are used to fuel cars and aeroplanes, power electricity plants, and heat our homes. 

They are also used to make medicines, cosmetics, plastics, synthetic fabrics, and lubricants. When you brushed your teeth today, you used a product made from oil – toothpaste.

We need a home as it gives shelter and security.

Hence the option D is correct.

Coal is _________ fuel.

evs substances in daily use can all changes be reversed? substances and objects changes around us

  1. fossil

  2. natural

  3. Both a and b

  4. None of these

Show answer
Correct Option: A
Explanation:

Coal is a fossil fuel. Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. 

Petroleum products are used for :

evs substances in daily use can all changes be reversed? substances and objects changes around us

  1. fuel purpose

  2. making creams and ointments

  3. both $A$ and $B$

  4. None of these

Show answer
Correct Option: C
Explanation:

Petroleum products such as petrol, diesel, kerosene and petroleum gas are used as fuel as they have high calorific value. 


Petroleum products are also used as raw material for cosmetics industries.

Hence the option C is correct.

The fuel used in homes for making food is :

evs substances in daily use can all changes be reversed? substances and objects changes around us

  1. CNG

  2. LPG

  3. KPG

  4. HDG

Show answer
Correct Option: B
Explanation:

B, LPG is clean fuel, it has high calorific value and low ignition temperature.

It is easy to handle and to transport. All these qualities make it suitable for domestic use.

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