NIOS Class 10th Science (212) in English Most Important Questions & Answers


Q.1 Give the common unit to measure our body temperature and write its SI unit.

Ans :

  • The body temperature is the amount of heat contained within the body.
  • The temperature of a body is referred to as the heat transfer from the body to the calorimeter (viz. thermometer).
  • Generally, the common unit to measure body temperature is degree celsius.
  • The SI unit of temperature is Kelvin.

Q.2 What are the advantages of SI units?

Ans :

  • There are a number of advantages of SI unit and the most important is that only one unit is used for each type of measurement.
  • The other advantages are as follows:
  • It is derived from basic units and so no further interconversion is necessary.
  • It is easily expressed as powers of ten in the metric system.

Q.3 How many molecules of O2 are in 8.0g of oxygen? If the O2 molecules were completely split into O (Oxygen atoms), how many mole of atoms of oxygen would be obtained?

Ans : Here we have to find out the mole of atoms of oxygen.

We have to find out the molecules of O2 

N(O2) = W/M N(O2)= 8/32

n(O2) = 0.25 mol.

Now as No. of O2 molecules are –

N(O2) = 0.25 x 6.022 x 1023

N(O2) = 1.505×1023 molecules

If all O2 molecules are split into O atoms , moles of  O -atoms are

n(O) = 2 × n(O2)

n(O) = 2 × 0.25

n(O) = 0.5 mol

Q.4 What does a chemical formula of a compound represents?

Ans : If we have given the chemical formula of a particular compound then basically it represents the number of different type of atoms in its molecule. It helps us to acknowledge the right compound.

Q.5 Assume that human body is 80% water. Calculate the number of molecules of water that are present in the body of a person whose weight is 65 kg.

Ans : Here we have to find out the number of molecules of water that are still present in the body of that person having weight of 65 kg.

80/100 *65 = mass of water

M/Mass of Water = n/N2

52/18 x Na = 26/9 x Na

= 1.739*1022


Discuss the merits of the modern periodic table.

Ans :

  1. The element designation is based on the atomic number, which is a simpler property.
  2. As the designation is on the basis of the atomic number, the rationale for putting isotopes at one position is justified.
  3. This describes the frequency of the elements’ properties and compares them to their electrical configurations.
  4. On the basis of the atomic number, the location of the elements that were mismatched on the basis of mass number (anomalous pairs such as argon and potassium) may be justified.
  5. The lanthanides and actinides at the bottom of the periodic table are arranged separately.

Q.7 The table is a simple, systematic and simple way to recall the characteristics of different components, since it is based on electronic configuration.Q.7 List the merits of the long form of the modern periodic table and explain any two of them.

Ans : Merits of long form of periodic table or modern periodic table are:

  • It is based on atomic numbers of elements.
  • It removes all of the defects of Mendeleev’s periodic table.
  • It relate position of elements on the basis of their electronic configuration.

Modern periodic table states that chemical and physical properties of elements are periodic function of their atomic numbers. Elements are arranged on the basis of their increasing energy levels with increasing periods.

Q.8 State Newlands’ law of octaves.

Ans : Newland’s law of octaves was given in 1865. It states, if elements are arranged according to their atomic weights, elements with similar properties will repeat after every 7 elements.

Q.9  State Newton’s third law of motion. Why it is difficult for a fireman to hold a hose pipe which ejects larger amount of water at a high speed?

Ans : Newton’s  third law states that for every action (force) in nature there is an equal and opposite reaction. In other words, if object a exerts a force on object b, then object b also exerts an equal and opposite force on object a.

Q.10 What is the relation between thrust and pressure? State the SI units of thrust and pressure. Why a camel can run in a desert easily?

Ans : Due to their broad feet, camels can walk readily in the desert. Their broad feet enable their body’s weight to behave on a bigger ground surface, decreasing the camel’s stress on the ground.
We can tell this because we understand there is an inverse proportion of stress and region.

Q.11 Define momentum. How the rate of change of momentum is related to force?
Ans :
Momentum is a concept in physics which refers to the measure of movement in an object. The energy is given by a sports team that is on the move. It is conceivable to describe force as mass moving. There is mass for all objects; so in the event that an item moves, at that point it has energy – it has its mass moving.

Q.12 An object of mass 2 kg travelling in a straight line with a velocity of .10ms-1 collides with and sticks to a stationary object of mass 6 kg. Then they both move off together in the same straight line. Calculate the total momentum just before the impact and just after the impact.

Ans :

Q.13  How does the gravitational force between two objects change if the masses of both objects are doubled?

Ans : If the volume of one of the objects is doubled, then the force of gravity between them is doubled. Therefore gravitational force is oppositely proportional to the square of the desperation distance between the two interacting objects, higher separation distance will result in lower gravitational forces.

Q.14 Write the equations of motion of an object moving or falling only under gravity.

Ans : Here g is constant near the exterior of earth. Therefore, all the equations for evenly accelerated motion of objects become valid when acceleration is recouped by g.

v = u + gt …….1

s = ut + 1/2 gt 2 …….2

V 2 = u 2  + 2gs …….3

Q.15 What is the mass of an object whose weight is 49N? (Given g = 9.8 ms−2).

Ans : Weight of the object W= 49 N

Mass of the object m =?

Acceleration due to gravity g=9.8m/s2

Now putting the values in the formula

W= m x g

49= m × 9.8

m= 49/9.8

m= 5 kg

thus mass of the object is 5 kilograms.

Q.16  State Archimedes’ principle. Give two applications of Archimedes’ principle.

Ans : Archimedes ' principle states that, when a body is absorbed completely or partially in a fluid, it practices an upward force that is equal to the weight of the liquid displaced by it. Applications:

1) It is used in architecture ships and submarines.

2) It is used in making lactometers that are used to determine the purity of milk.

Q.17 State Law of Conservation of Energy. Explain with the help of examples.

Ans : The law of conservation of energy states that energy can neither be created nor destroyed – only converted from one form of energy to another. This means that a system always has the same amount of energy, unless it’s added from the outside. The principle of energy conservation states that energy is neither created nor destroyed. It may transform from one type to another. The law of conservation of energy can be seen in these everyday examples of energy transference: Water can produce electricity. Water falls from the sky, converting potential energy to kinetic energy. This energy is then used to rotate the turbine of a generator to produce electricity.

The phenomenon of converting one form of energy to another form is called energy transformation.

Potential energy of water stored in a dam changes into kinetic energy as water falls from a height. The kinetic energy of flowing water changes into kinetic energy of rotation of a turbine. The coil attached with the shaft of the turbine rotates in a magnetic field to convert kinetic energy of rotation of the turbine into electrical energy.

In our homes an electric bulb (or tube light) converts electrical energy into light energy, electric oven (or heater or iron or soldering iron) convert electrical energy into heat energy and electric pump (or motor) converts electrical energy into mechanical energy.

An electric cell converts chemical energy into electrical energy; solar cell converts light energy into electrical energy and a thermocouple changes heat energy into electric energy.

A microphone converts sound energy into electrical energy and a loudspeaker changes electrical energy into sound energy.

Heat engine converts heat energy into work (mechanical energy) and work done against friction is converted into heat.

During transformation of energy from one form to another it remains constant. This is known as Law of Conservation of Energy.

Q.18 Why road accidents at high speeds are much worse than the accidents at low speeds?

Ans : Vehicles with high speeds have high momenta. When they come to rest in very small time they experience high forces we know that rate of change of momentum is force, lower the time higher is force. The road accidents are damaging in high speed because the incessant velocity of the speed is high it also increases the momentum of the moving object and when it collides with an impeccable force is immensely strong As a result the reactionary pressure is equally strong causing lot of damage.

Q.19 A ball of mass 0.5 kg has100 J of kinetic energy. What is the velocity of the ball?

Ans : If the mass has units of kilograms and the velocity of meters per second, the kinetic energy has units of kilograms-meters squared per second squared.

K.E. =  mv2.

Where m is the mass of the object in kilograms, KE is the kinetic energy in Joules, velocity v is expressed in metres per second.

Give 100 =  0.5v2

V2 = 100.2/0.5 = 400

Q.20  Two bodies of equal mass move with uniform velocities u and 4 u respectively. Find the ratio of their kinetic energies.

Ans : Let mass of 2 bodies be m

Hence velocity of 1st body is u and

Velocity of 2nd body is 4u

Kinetic energy of 1st body = 1/2mu²

Kinetic energy of 2nd body = 1/2m(4u)²

Thus we will get ratio as 1/16.

Q.21 Does a convex lens always converge light? Explain.

Ans : Yes , convex lens always converge light and it is because of the property of the convex lens. In this lens thickness is on the center and it converges all the light that are incident on it.

So convex lens always converge light as it has the property of converging light.

Q.22 An object is placed infront of a plane mirror. The mirror is moved away from the object with the speed of 0.25 ms–1. What is the speed of the image with respect to the mirror and with respect to the object?

Ans : Here we have given from the data:-

u = 0.25 m/s

Image speed wrt to the mirror = u = 0.25 m/s

Here at the last speed of the image wrt. tot the mirror

= 2u = 2 x 0.25 = 0.5 m/s

Q.23 Distinguish visible, ultraviolet and infrared light.

Ans : Visible light:- In visible light there the frequency is going to be very low and EM radiation is already very low in that. Visible light is measured in flux (lumens per square meter) or foot-candles (fc).

Ultraviolet light:- Ultra violet light units in microwatts of UV radiation lumen of the visible light energy of UV radiation is particularly damaging to the body. It is invisible and human eye not able to see.

Infrared light:- It is the different type of energy which human naked eye can’t see but we can fell the hotness of the infrared light. All things in the world is emitting some infrared light from itself.

Q.24  Find the position of the image formed in concave mirror of focal length 12 cm when object is placed 20 cm away from the mirror. Also find magnification.

Ans : As per the given data from the question:-

Focal length is given as F= 12cm

Object distance= u= 20cm

Now the image distance we will assumed as =V

According to the formula:-

 =  +

As we are going to put the values, we get


Therefore the image distance= 30cm

Magnification = -v/u

Now putting the values.

So We will get the magnification= -1.5

Q.25 Write three sentences on why we need to classify and give scientific names to organisms.

Ans : Every species would get a name consisting of two words: the first word was the genus, and the second word was a specific epithet, and that couplet would together uniquely identify the species.

For example, modern humans belong to the genus Homo and within this genus to the species Homo sapiens.

Q.26 List 10 ways in which organisms help each other survive in nature. What message can you derive from their interdependence?

Ans : Every organism has a unique ecosystem within which it lives. This ecosystem is its natural habitat. This is where the basic needs of the organism to survive are met: food, water, shelter from the weather and place to breed its young. All organisms need to adapt to their habitat to be able to survive.

Adaptation is basically the modification of an organism or its parts that is a basic principle of evolution. An adaptation is an inherited characteristic that helps an organism survive and reproduce in its environment. Birds show the same diversity of lifestyles as mammals, but they also show some unique adaptations.

Some creatures, like the apple snail, can survive in different ecosystems- from swamps, ditches and ponds to lakes and rivers. It has a lung/gills combination that reflects its adaptation to habitats with oxygen poor water. This is often the case in swamps and shallow waters.

The flora in forests also helps establish a protection around animals living within them. This protection is offered both within and outside the ecosystem. For example, trees and large bushes help protect animals from their predators, by providing a camouflage. Animals are also protected to certain degree from outside influences like extreme weather and climates by this. Apart from these, there is also the obvious fact that forests are home to a variety of animals.

Forests are an ecosystem and, in all ecosystems, living organisms are interdependent on each other to resume their existence.

Q.27 Name the three domains of life and state one distinguishing features of each.

Ans : Archaea, any of a group of single-celled prokaryotic organisms (that is, organisms whose cells lack a defined nucleus) that have distinct molecular characteristics separating them from bacteria (the other, more prominent group of prokaryotes) as well as from eukaryotes (organisms, including plants and animals, whose cells contain a defined nucleus).

Prokaryote, also spelled procaryote, any organism that lacks a distinct nucleus and other organelles due to the absence of internal membranes. Bacteria are among the best-known prokaryotic organisms.

Eukaryote, any cell or organism that possesses a clearly defined nucleus. The eukaryotic cell has a nuclear membrane that surrounds the nucleus, in which the well-defined chromosomes (bodies containing the hereditary material) are located. Eukaryotic cells also contain organelles, including mitochondria (cellular energy exchangers), a Golgi apparatus (secretory device), an endoplasmic reticulum (a canal-like system of membranes within the cell), and lysosomes (digestive apparatus within many cell types).

Q.28 Where does the digestion of starch, proteins and fats take place and what is the  role played in digestion by liver and pancreas?

Ans : Most of fat digestion happens once it resides the small intestine. Also the majority of nutrients are absorbed. The pancreas produces enzymes that break down fats, carbohydrates, and proteins. Liver produces bile that helps you digest fats and certain vitamins.

Q.29 What is a balanced diet? Name three items of a diet that provide three different nutrients?

Ans : A diet is all that we consume in a day. And a balanced diet is a diet that contains an adequate quantity of the nutrients that we require in a day. A balanced diet includes six main nutrients, i.e. Fats, Protein, Carbohydrates, Fibre, Vitamins, and Minerals.

A balance diet provides the body essential nutrition: fluid,adequate amino acids from proteins, essential fatty acids, vitamins, minerals,fibres and adequate calories.

Healthy foods include:

  1. Fat-free and low-fat dairy products, such as low-fat yoghurt, cheese, and milk.
  2. Protein foods, such as lean meat, fish, poultry without skin, beans, and peas.
  3. Whole-grain foods, such as whole-wheat bread, oatmeal, and brown rice. …
  4. Fresh fruits, canned, frozen, or dried.

Q.30  Explain how oxygen leaves the blood from the tissue capillaries and carbon dioxide enters the blood in the tissue capillaries.

Ans : When we breathe in, we take in O2 , which reaches the lung alveoli. O2 then diffuses into blood of the surrounding capillaries from the alveoli, which has a high concentration of O2 by diffusion. After supplying O2 to the body cells, the blood collects CO2 , which is produced after cellular respiration in the cells.

Q.31 Describe the three regions of the brain.

Ans : The three main regions of the brain are:

  • Cerebrum: it is the uppermost part containing two separate hemispheres. Its main function is to maintain movements, sensation, vision, hearing, memories, smell, taste, etc. it is the sub-conscious are of the brain.
  • Cerebellum: Major region of hindbrain located near brainstem its main function is to maintain balance, coordination and body posture.
  • Brainstem: it consists of the midbrain, pons, and medulla oblongata. It is the most distal part of the brain.

Q.32 What is the nature of the membranes covering the brain? What is the name of the fluid that fills the space between these membranes? What is its role?

Ans : Meninges is the covering of the brain and spinal cord. It is made up of three layers:

There are three layers of meninges:

  • Dura mater, which is closest to the bone.
  • Arachnoid, which is loosely around the brain.
  • Pia mater, which is closely attached to the brain and spinal cord surface.

Q.33 Give one function performed by each of the following:

1. Cerebrum

Ans : The cerebrum maintains movement, speech, vision, memory, etc.


Ans : Cerebellum maintains balance, coordination, and body posture.


Ans : Hypothalamus maintains homeostasis and regulates hormone secretion.

Medulla oblongata regulates breathing, sneezing, and respiration.

4. Cerebrospinal fluid

Ans : Cerebrospinal fluid provides nutrition to nervous tissue.

Q.34 Mention two differences between asexual and sexual modes of reproduction?

Ans : The two difference between sexual and asexual reproduction is basically the mode of reproduction:-


Q.35 Trace the events after pollination that lead to seed formation

Ans : After pollination, when pollen is going to landed on the stigma of a suitable flower of the same species, can a chain of events happen that ends in the making of seeds. A pollen grain on the stigma grows a tiny tube, all the way down the style to the ovary. The ovary develops into a fruit to protect the seed.

Q.36 How is a callus developed in tissue culture? Give the steps.

Ans : So, these are the types of plant tissue culture:

  1. Cell or suspension culture.
  2. Explant culture.
  3. Callus culture.
  4. Protoplast culture.
  5. Embryo culture.
  6. Anther and pollen culture.
  7. Ovule culture.
  8. Ovary culture.

The callus obtained from incubation of ex plant is transferred into another medium and re incubated. Plant tissue culture is an in-vitro culture of plant cells, tissues or organs which will form a complete plant.

Plant tissue culture works on the basis of impotency. It is the ability of a plant cell to form the complete plant through differentiation and re differentiation.

Q.37 Compare the physical properties of diamond and graphite.

Ans : Diamond

  1. The geometry is tetrahedral. C – C bond length is 154 pm
  2. It has rigid covalent boning which is difficult to break.
  3. It is an electrical insulator.


  1. The geometry is planar C – C bond length is 141.5 pm
  2. It is soft. Its layers can be separated easily.
  3. It is good conductor of electricity.

Q.38 What is a homologous series?

Ans : A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by CH2 group.

Example of Homologous series : All the alkanes have similar structures with single covalent bonds and show similar chemical properties, so they can be grouped together in the form of a homologous series.

Homologous series of alkanes : Methane, CH4 ; Ethane, C2H6 ; Propane, C3H8 ; Butane, C4H10 ; Pentane, C5H12

Q.39 Draw the Chemical Structure of Butane and Isobutane and based on it justify that they are isomers.

Ans :

Butane is an alkane with four carbon atoms so molecular formula is C4H10. It has two isomers; n-butane and isobutane. Here n-butane is a straight-chain compound with four carbon atoms bonded with single covalent bonds.

Q.40 What is the difference between the structure of an aldehyde and a ketone?

Ans : Aldehydes have the double bond at the end of the molecule. That means the carbon at the end of the chain has a double bond to an oxygen atom. Ketones have the double bond anywhere in the molecule except for the end. That means you will see a double bond to oxygen from one of the carbon atoms in the middle of the chain.

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