Class 10th NCRT BOOK QUESTIONS AND ANSWER SOLUTION ALL CHAPTERS PDF

1. Why should a magnesium ribbon be cleaned before burning in the air?

Solution:

Magnesium ribbon should be cleaned before burning in air because Magnesium metal reacts with the atmospheric

oxygen and forms Magnesium Oxide (MgO) layer which is a very stable compound. In order to prevent further

reactions with Oxygen, it is therefore necessary to clean the ribbon by to remove the layer of MgO.

2. Write a balanced equation for the following chemical reactions.

i) Hydrogen + Chloride —-> Hydrogen chloride

ii) Barium chloride + Aluminium sulphate —-> Barium sulphate + Aluminium chloride

iii) Sodium + Water —-> Sodium hydroxide + Hydrogen

Solution:

i) H2+ Cl2→ 2HCl

ii) 3BaCl2+ Al2(SO4)3→3BaSO4+ 2AlCl3

iii) 2Na + 2H2O → 2NaOH + H2

3. Write a balanced chemical equation with state symbols for the following reactions

i) Solutions of Barium chloride and Sodium sulphate in water react to give insoluble Barium sulphate and

solution of Sodium chloride.

ii) Sodium hydroxide solution in water reacts with the hydrochloric acid solution to produce Sodium chloride

solution and water.

Solution:

i) BaCl2+ Na2SO4→ BaSO4+ 2NaCl

ii) NaOH + HCl → NaCl + H2O

Download PDF CHAPTER 1

1. A solution of a substance, ‘X,’ is used for whitewashing.

(i) Name the substance ‘X’ and write its formula.

(ii) Write the reaction of the substance ‘X’ named in (i) above with water.

Solution:

i) The substance ‘X’ which is used in whitewashing is quick lime or Calcium Oxide and its formula is CaO.

ii) CaO + H2O → Ca(OH)2

2. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double the amount collected in the

other? Name this gas.

Solution:

In activity 1.7, gas collected in one of the test tubes is double of the amount collected in the other because water gets

hydrolysed to release H2 and O2 gas. Here, after electrolysis two molecules of Hydrogen and one molecule of oxygen

gas are released; hence, the amount of Hydrogen collected would be double than that of oxygen.

1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Solution:

When an iron nail is dipped in the copper sulphate solution, iron displaces copper from the copper sulphate because

iron is more reactive than copper. Therefore, the colour of the copper sulphate solution changes. The reaction is

Fe + CuSO4 → FeSO4 + Cu

2. Give an example of a double displacement reaction other than the one given in Activity 1.10.

Solution:

Reaction Between silver nitrate (AgNO3) and Sodium chloride (NaCl) is an example of a double displacement reaction.

During the reaction, negative and positive ions trade positions as a result of the formation of white silver chloride

precipitate. The chemical reaction is given below.

Ag+ + NO3

– + Na+ + Cl–→ AgCl + Na+ + NO3

–

3. Identify the substances that are oxidised and that are reduced in the following equation.

i) 4Na(s) + O2(g) → 2Na2O(s)

ii) CuO(s) + H2(g) → Cu(s) + H2O(l)

Solution:

The Sodium (Na) in the first equation is getting oxidized with the addition of Oxygen (O2), and the Copper (Cu) in the

second equation is reduced due to the addition of Hydrogen (H2).

1. Which of the statements about the reaction below are incorrect?

2PbO(s) + C(s) → 2Pb(s) + CO2(g)

(a) Lead is getting reduced

(b) Carbon Dioxide is getting oxidised

(d) Lead oxide is getting reduced

(i) (a) and (b)

(ii) (a) and (c)

(iii) (a), (b) and (c)

(iv) all the above

Solution:

(i) (a) and (b)

Explanation: (a) Because Oxygen is being removed and (b) Because the removed oxygen from Lead is added to the

elemental Carbon.

2. Fe2O3+ 2Al → Al2O3+ 2Fe

The above reaction is an example of a

1. Combination reaction

2. Double displacement reaction

3. Decomposition reaction

4. Displacement reaction

Solution:

The answer is 4. Displacement reaction.

Explanation: The Oxygen from the Ferrous oxide is getting displaced to the Aluminium metal to form Aluminium

Oxide. In this reaction, Aluminum is a more reactive metal than Fe. Therefore, Al will displace Fe from its oxide. This

type of chemical reaction, called displacement reaction, is in which one of the elements displaces another. Here, less

reactive metal is displaced by more reactive metal. Since one-time displacement is occurring, it is called a single

displacement reaction.

3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.

1. Hydrogen gas and Iron chloride are produced.

2. Chlorine gas and Iron hydroxide are produced.

3. No reaction takes place.

4. Iron salt and water are produced.

CHAPTER 2

Acids Bases and Salts

DOWNLOAD PDF CHAPTER 2

In-text questions set 1

Page number 18

1. You are given three test tubes. The three test tubes contain distilled water, an acidic solution and the basic

solution, respectively. There is only red litmus paper available in order to identify what is there in each test tube.

How will you find out what is in each of the test tubes?

Solution: We can identify the content in each of the test tubes using red litmus paper. This can be done by noticing the

colour change of the red litmus paper.

 On litmus paper, the three solutions in the test tubes are poured separately.

 The solution which turns red litmus to blue contains a basic solution.

 Divide the formed blue litmus paper into two parts.

 The solution from the test tube, which turns blue litmus paper to red, will be the acidic solution.

 The solution of the test tube, which does not change either red or blue litmus paper, contains water.

NOTE: After immediate distillation, distilled water has a pH of 7. However, within a few hours after distillation, it

absorbs carbon dioxide from the atmosphere and turns slightly acidic with a pH of 5.8. Page number 18

In-text questions set 2

Page number 22

1. Why should curd and sour substances not be kept in brass and copper vessels?

Solution: Curd and sour food substances contain acids; these acidic substances combine with metal. This reaction turns

food into poison, which damages people’s health.

2. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test

for the presence of this gas?

Solution: When an acid reacts with any metal, salt and hydrogen gas are formed.

Metal + Acid → Salt + Hydrogen gas

3. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved

extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds

formed is calcium chloride.

Solution: As the metal compound released is Calcium Chloride, the gas evolved here is CO2. Hence, metal A should be

Calcium Carbonate. Hence, the reaction between Calcium Carbonate and HCl is

CaCO3 (s) + 2HCl (Aq) → CaCl2( Aq) + CO2 (g) + H2O (l)

In-text questions set 3

Page number – 25

1. Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like

alcohol and glucose do not show an acidic character?

Solution: Release of H+

ion in water will make a compound acidic or non-acidic. Acids are substances which, upon

dissociating with water, resulting in the production of Hydrogen ions. Some compounds show an acidic character as

they dissociate in the aqueous solution, which results in the production of hydrogen ions (acids like HCl, HNO3).

Compounds similar to glucose or alcohol do contain a hydrogen element, but they do not show signs of acidic nature.

The fact is that the hydrogen in them will not separate from like the hydrogen in the acids. They will not separate to

become hydrogen ions, on dissolving in the water.

2. Why does an aqueous solution of acid conduct electricity?

Solution: Charged particles are responsible for the conductance of electricity in an acid. These charged particles, called

ions, are the reason behind the conductance of electricity in acid.

3. Why does dry HCl gas not change the colour of the dry litmus paper?

Solution: HCl does not give out Hydrogen ions; therefore, HCl does not show any acidic behaviour, and the colour of

the litmus paper remains the same on reacting with HCl gas.

4. While diluting an acid, why is it recommended that the acid should be added to water and not water to the

acid?

Solution: While diluting an acid, it is recommended that the acid should be added to water and not water to the acid

because if water is added to a concentrated acid, it releases a huge amount of heat which may result in an explosion and

can cause acid burns on the face, clothes and body parts. Hence, it is safe to add acid to water but not water to acid.

5. How is the concentration of hydronium ions (H3O+

) affected when a solution of an acid is diluted?

Solution: When acid is added to water, there will be a fixed amount of hydronium present in the fixed volume of the

solution. If we dilute the solution, hydronium ions per volume of the solution decrease, and this, in turn, decreases

Hydronium concentration in the solution.

6. How is the concentration of hydroxide ions (OH–

) affected when excess base is dissolved in a solution of

sodium hydroxide?

Solution: When a base is dissolved in sodium hydroxide solution, its hydroxide ions increase, but it will reach

saturation at some point. After saturation point, hydroxide ion concentration is not affected even after adding base

further.

CHAPTER 3

Metals and Non-metals

DOWNLOAD PDF CHAPTER 3

In-text questions set 1 Page number 40

1. Give an example of a metal which

(i) Is a liquid at room temperature?

(ii) Can be easily cut with a knife?

(iii) Is the best conductor of heat?

(iv) Is a poor conductor of heat?

Solution:

(i) Mercury is the metal which is liquid at room temperature

(ii) Sodium and potassium are the metals which can be cut with a knife

(iii) Silver is the best conductor of heat

(iv) Mercury and lead are poor conductor of heat.

2. Explain the meanings of malleable and ductile.

Solution:

1. Metals which can be beaten to sheets are said to be malleable

2. Metals which can be drawn into thin wires are said to be ductile

In-text questions set 2

Page number 46

1. Why is sodium kept immersed in kerosene oil?

Solution: Sodium is a reactive metal. If kept open it will react with oxygen to explore and catch fire. Sodium metal is

kept immersed in kerosene to prevent their reaction with oxygen, moisture and carbon dioxide of air.

2. Write equations for the reactions of

(i) iron with steam

(ii) calcium and potassium with water

Solution: (i) Iron reacts with steam to form a magnetic oxide of Fe with the liberation of H2.

3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)

(ii) Calcium reacts with water to form calcium hydroxide and hydrogen.

Ca(s) + 2H2O(I) → Ca(OH)2(aq) + H2(g)

Potassium reacts with cold water violently immediately with evolution of H2 which catches fire.

2K(s) + 2H2O(I) → 2KOH(aq) + 2H2(g)

(i) Metal B is the most reactive as it gives displacement reaction with iron (II) sulphate.

(ii) When metal B is added to copper (II) sulphate solution, a displacement reaction will take place because of which

the blue colour of copper (II) sulphate solution will fade and a red-brown deposit of copper will be formed on metal B.

(iii)Metal B is the most reactive because it displaces iron from its salt solution. Metal A is less reactive because it

displaces copper from its salt solution. Metal C is still less reactive because it can displace only silver from its salt

solution, and metal D is the least reactive because it cannot displace any metal from its salt solution. Hence, the

decreasing order of reactivity of the metals is B > A > C > D.

4. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical

reaction when iron reacts with dilute H2SO4.

Solution: Hydrogen gas is liberated when dilute HCl is added to a reactive metal.

Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g)

5. What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction

that takes place.

Solution: Zinc is more reactive (more electro positive) than iron. Therefore, Zinc displaces Iron from its salt solution.

The colour of ferrous sulphate is pale green, which turns colourless.

FeSO4 + Zn → ZnSO4 + Fe(s)

Light green Zinc sulphate(Colourless)

CHAPTER 4

Carbon and Its Compounds

DOWNLOAD PDF CHAPTER 4

Exercise questions Page Number: 77-78

1. Ethane, with the molecular formula C2H6, has

(a) 6 covalent bonds

(b) 7 covalent bonds

(d) 9 covalent bonds

Answer: (b) 7 covalent bonds

Solution: Ethane, with the molecular formula C2H6, has 7 covalent bonds.

2. Butanone is a four-carbon compound with the functional group

(a) carboxylic acid

(b) aldehyde

(d) alcohol

Answer: (c) ketone

3. While cooking, if the bottom of the vessel is getting blackened on the outside, it means that

(a) the food is not cooked completely

(b) the fuel is not burning completely

(d) the fuel is burning completely

Answer: (b) the fuel is not burning completely

Solution: While cooking, if the bottom of the vessel is getting blackened on the outside indicates that the fuel is not

burning completely.

4. Explain the nature of the covalent bond using the bond formation in CH3Cl.

Solution: Carbon can neither lose 4 electrons nor gain four electrons as these processes make the system unstable due

to the requirement of extra energy. Therefore, CH3Cl completes its octet configuration by sharing its 4 electrons with

carbon atoms or with atoms of other elements. Hence, the bonding that exists in CH3Cl is a covalent bonding.

Here, carbon requires 4 electrons to complete its octet, while each hydrogen atom requires one electron to complete its

duplet. Also, chlorine requires an electron to complete the octet. Therefore, all of these share electrons, and as a result,

carbon forms 3 bonds with hydrogen and one with chlorine.

5. Draw the electron dot structures for

(a) ethanoic acid

(b) H2 S

6. What is a homologous series? Explain with an example.

A homologous series is a series of compounds which has the same functional group. This also contains a similar

general formula and chemical properties. Since there is a change in the physical properties, we can say that there would

be an increase in molecular size and mass.

For example, methane, ethane, propane, butane, etc., are all part of the alkane homologous series. The general formula

of this series is CnH2n+2. Methane CH4 Ethane CH3CH3 Propane CH3CH2CH3 Butane CH3CH2CH2CH3. It can be noticed

that there is a difference of −CH2 unit between each successive compound.

9. Why are carbon and its compounds used as fuels for most applications?

Solution: Carbon and its compounds are used as fuels for most applications because they have high calorific values and

give out a lot of energy. Most of carbon compounds give a lot of heat and light when burnt in the air.

10. Explain the formation of scum when hard water is treated with soap.

Solution: Scum is produced from the reaction of hard water with soap. Calcium and magnesium present in the hard

water form an insoluble precipitate called scum.

11. What change will you observe if you test soap with litmus paper (red and blue)?

Solution: When soap is dissolved in water due to the formation of alkaline NaOH or KOH, the solution is alkaline. The

solution changes the colour of the red litmus to blue, but in the soap solution, the blue litmus remains blue.

12. What is hydrogenation? What is its industrial application?

Solution: Hydrogenation is a process or a chemical reaction between hydrogen and other compounds. It is usually done

in the presence of catalysts. For example, nickel, palladium or platinum. Hydrogenation is used mainly to saturate

organic compounds.

13. Which of the following hydrocarbons undergo addition reactions: C2H6, C3H8, C3H6, C2H2 and CH4?

Solution: Unsaturated hydrocarbons undergo addition reactions. C3H6 and C2H2 are unsaturated hydrocarbons which

undergo addition reactions.

14. Give a test that can be used to differentiate between saturated and unsaturated hydrocarbons.

Solution: The bromine water test is used to differentiate between the unsaturated compounds (like alkenes and alkynes)

and the saturated compounds. For this purpose, bromine is used in the form of bromine water. A solution of bromine in

water is called bromine water. Bromine water has a red-brown colour due to the presence of bromine in it. When

bromine water is added to an unsaturated compound, then bromine gets added to the unsaturated compound, and the

red-brown colour of bromine water is discharged. So, if an organic compound decolourises bromine water, then it will

be an unsaturated hydrocarbon (containing a double bond or a triple bond), but saturated hydrocarbons (alkanes) do not

decolourise bromine water.

The bromine water test is performed to differentiate between the unsaturated compounds (like alkenes and alkynes) and

the saturated compounds. When bromine water is added to an unsaturated hydrocarbon, the red-brown colour of the

bromine solution is discharged. So, if there is dis-colouration, then the compound will be an unsaturated hydrocarbon.

15. Explain the mechanism of the cleaning action of soaps.

Solution: There are so many impurities and dirt mixed in water, and most of all, the dirt does not dissolve in the water.

Soap molecules are a combination of salts such as sodium or potassium. The molecules are of a long chain of

carboxylic acids. So, when the carbon chain is dissolved in oil and the ionic end is dissolved in the water, the soap

starts cleansing and trapping the dirt. When this happens, the soap molecules form structures called micelles that are

used for capturing the oil droplets, and then the other end is the ionic faces. This will then form an emulsion in water

and help in dissolving the dirt or impurities when the clothes are washed.

CHAPTER 5

Periodic Classification of Elements

DOWNLOAD PDF CHAPTER 5

Questions Page Number: 81

1. Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.

Solution:

Döbereiner’s triads did exist in the columns of Newlands’ Octaves; For example, the elements

Lithium (Li), Potassium (K) and Sodium (Na) constitute a Dobereiner’s Triad but are also found in the second column

of Newland’s Octaves.

2. What were the limitations of Döbereiner’s classification?

Solution:

(i) They were not applicable for very low mass or very high mass elements.

(ii) All the elements couldn’t fit into Dobereiner’s triads.

(iii) As the methods to calculate atomic mass improved, Dobereiner’s triads’ validity began to decrease. For example,

in the triad of F, Cl and Br, the arithmetic mean of atomic masses of F and Br is not equal to the atomic mass of CI.

3. What were the limitations of Newlands’ Law of Octaves?

Solution:

Limitations of Newlands’ Law of Octaves are as follows:

 Newlands’ Law of Octaves is applicable only to elements up to Calcium

 Newland assumed there were 56 elements in nature and no more elements would be discovered in the future.

 To fit elements into the table, Newland put two elements into one slot. Newland introduced unlike elements

with different properties into one column.

 Iron (Fe) was placed away from elements that resemble in properties. Ex: Nickel and cobalt

Questions Page Number: 85

1. Use Mendeleev’s Periodic Table to predict the formulae for the oxides of the following elements: K, C, AI, Si,

Ba.

Solution:

K- K2O

C-C2O4 or CO2

Al- Al2O3

Si-Si2O4 or SiO2

Ba2O2 or BaO

Oxygen is a member of group VI A in Mendeleev’s periodic table. Its valency is 2. Similarly, the valencies of all the

elements listed can be predicted from their respective groups. This will help in writing the formulae of their oxides.

(i) Potassium (K) is a member of group IA. Its valency is 1. Therefore, its formula is K2O.

(ii) Carbon (C) is a member of group IV A. Its valency is 4. Therefore, the formula is C2O4 or CO2.

(iii) Aluminium (Al) belongs to groups III A and its valency is 3. The formula of its oxide is Al2O3.

(iv) Silicon (Si) is present in group IV A after carbon. Its valency is also 4. The formula of oxide is Si2O4 or SiO2.

(v) Barium (Ba) belongs to group II A and the valency of the element is 2. The formula of the oxide of the element is

Ba2O2 or BaO.

2. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic

Table? (Any two)

Solution:

Germanium and Scandium are the elements that are left by Mendeleev in his Periodic Table since its discovery.

3. What were the criteria used by Mendeleev in creating his Periodic Table?

Solution:

Mendeleev concentrated on various compounds formed by the elements with Hydrogen and Oxygen. Among physical

properties, he observed the relationship between the atomic masses of various elements while creating his periodic

table.

4. Why do you think the noble gases are placed in a separate group?

Solution:

Noble gases are placed in a separate group because of their inert nature and low concentration in our atmosphere. They

are kept in a separate group called the Zero group so that they don’t disturb the existing order.

Questions Page Number: 90

1. How could the Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table?

Solution:

(a) In the Modern Periodic table, elements are arranged in the increasing order of their atomic number. This removes

the anomaly regarding certain pairs of elements in Mendeleev’s periodic table.

(b) The Atomic number of cobalt is 27, and that of nickel is 28. Hence, cobalt will come before nickel even though its

atomic mass is greater.

c) All isotopes of the same elements have different atomic masses but the same atomic number; therefore, they are

placed in the same position in the modern periodic table.

2. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for

your choice?

Solution:

Calcium and Beryllium are similar to Magnesium because all three elements belong to the same group and have 2

valence electrons in their outer shell.

3. Name

(a) Three elements that have a single electron in their outermost shells.

(b) Two elements that have two electrons in their outermost shells.

Solution:

1. Lithium (Li), Sodium (Na) and potassium (k) have a single electron in their outermost shells.

2. Magnesium (Mg) and Calcium (Ca) have two electrons in their outermost shells

3. Neon (Ne), Argon (Ar and Xenon (Xe) filled outermost shells

4. a) Lithium, sodium, and potassium are all metals that react with water to liberate hydrogen gas. Is there any

similarity in the atoms of these elements?

(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms

have in common?

Solution:

They’ve one valence electron in their outermost shells, and as a result of this, they are very unstable. So, they readily

react with water to liberate hydrogen. They are also called alkali metals.

Their outermost shells are full, leading to high stability. They react only in extreme circumstances and hence are called

noble gases

CHAPTER 6

Life Processes

DOWNLOAD PDF CHAPTER 6

Questions Page Number: 95

1. Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?

Solution:

Multi-cellular organisms like humans have very big bodies and require a lot of oxygen to diffuse into the body quickly

in order to meet the oxygen requirement. Diffusion is a slow process which will take a lot of time to circulate oxygen to

all the body cells. Because of its slow nature, diffusion is insufficient to meet the oxygen requirements of multicellular

organisms like humans.

2. What criteria do we use to decide whether something is alive?

Solution:

Walking, breathing, growth and other visible changes can be used to determine whether something is alive or dead.

However, some living things will have changes that are not visible to our eye; Hence, the presence of the life process is

a fundamental criterion to decide whether something is alive.

3. What are outside raw materials used for by an organism?

Solution:

The outside raw material is used by organisms for food and oxygen. Raw materials’ requirement varies on the

complexity of the organism and the environment it is living.

4. What processes would you consider essential for maintaining life?

Solution:

Life processes such as respiration, digestion, excretion, circulation and transportation are essential for maintaining life.

Questions Page Number: 110

1. What are the components of the transport system in human beings? What are the functions of these

components?

Solution:

The heart, blood and blood vessels are the main components of the transport system in human beings.

Functions of these components

Heart

The heart pumps oxygenated blood throughout the body. It receives deoxygenated blood from the various body parts

and sends impure blood to the lungs for oxygenation.

Blood

Blood transports oxygen, nutrients, CO2, and nitrogenous wastes.

Blood vessels

Blood vessels, arteries and veins carry blood to all parts of the body.

2. Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

Solution:

Mammals and birds are warm-blooded animals which keep their body temperature constant irrespective of the

environment they live. This process requires a lot of oxygen for more cellular respiration so that warm-blooded animals

produce more energy to balance their body temperature. Hence, it is very important for warm-blooded animals to

separate oxygenated and deoxygenated blood to keep their circulatory system efficient.

3. What are the components of the transport system in highly organised plants?

Solution:

There are two types of conducting tissues in highly organised plants that carry out the transport system 1) Xylem 2)

Phloem. Xylem conduct water and minerals from roots to the rest of the plant parts. Similarly, Phloem transports food

materials from the leaf to other parts of the plant.

4. How are water and minerals transported in plants?

Solution:

Xylem parts of the tracheids and vessels of roots, stems and leaves are interconnected to form a continuous system of

water-conducting channels that reaches all parts of the plant. Transpiration creates a suction pressure which forces

water into the xylem cells of roots. After this, there will be a steady movement of water from the root xylem to all parts

of the plant connected through conducting interconnected water-conducting channels.

5. How is food transported in plants?

Solution:

Food is transported in plants by a special organ called the phloem. Phloem transports food materials from leaves to

different parts of a plant. Transportation of food in phloem is achieved by the expenditure of energy from ATP. This

increases osmotic pressure in the tissue, causing water to move. This pressure moves material in the Phloem to the

tissues with less pressure. This helps in the transportation of food materials as per the needs. Example, Sucrose.

CHAPTER 7

Control and Coordination

DOWNLOAD PDF CHAPTER 7

Questions Page Number: 119

1. What is the difference between a reflex action and walking?

Solution:

Reflex actions are the involuntary actions that occur in response to stimuli. They occur without involvement of

conscious areas of brain. All the reflex actions are unconscious actions. Reflex action involves the brain and spinal cord

of central nervous systems.

On the other hand, voluntary actions are those which occur under the control of cerebellum of the brain. Walking is

learnt as we grow. Walking is controlled by the brain and is consciously used whenever required.

2. What happens at the synapse between two neurons?

Solution:

At the synapse between two neurons, electric signals are converted into chemicals that can easily cross over the gap and

pass on the chemical messenger to the next neuron where it is converted back to electrical signal.

3. Which part of the brain maintains the posture and equilibrium of the body?

Solution:

Cerebellum, which is a part of the brain, is responsible for controlling the motor functioning. Hence, it is the part

engaged in the maintenance of posture and equilibrium of the body.

4. How do we detect the smell of an agarbatti (incense stick)?

Solution:

The smell of an agarbatti is detected by the nose. The olfactory receptors present in the nose sends electrical signal to

the fore brain. The fore brain interprets this signal as the smell of the incense stick.

5. What is the role of the brain in reflex action?

Solution:

Reflex actions are formed instantaneously in response to a stimulus that has no time to think. For instance, the sensory

nerves that detect heat are connected to the nerves that move the muscles of the hand. Such a connection of detecting

the signal from the nerves (input) and responding to it quickly (output) is known as reflex arc.

Reflex action are generated in spinal cord and the information also reaches brain. This helps the brain to record this

event and remember it for future use. Brain helps the person to get awareness of the stimulus and prevent the danger

posed by the situation in the future.

8. Give an example of a plant hormone that promotes growth.

Solution:

Auxins and Gibberlins are the hormone responsible for the growth of plant.

Auxins are responsible for the cell elongation in shoot and also regulate growth.

Gibberlin is responsible for stem elongation and germination.

9. How do auxins promote the growth of a tendril around a support?

Solution:

Auxins are the plant hormones produced at the tips of shoots and roots. Auxins are present at the tip of tendrils. When

tendrils are attached around any support, their growth is slowed down as auxins are sensitive to touch. This makes them

10. Design an experiment to demonstrate hydrotropism.

Solution:

To demonstrate hydrotropism in plants.

Procedure:

i. Plant a seedling in a vessel containing soil.

ii. Adjacent to the seedling put a porous pot containing water.

iii. Leave the set up for few days.

Observation:

iv. On examining the roots, it is observed that the roots bend towards the source of water and do not grow straight.

Result:

It confirms that plants show hydrotropism as the roots bend towards the porous pot of water. As hydrotropism is a

plant-growth response in which the direction of growth is determined by a stimulus of gradient in water concentration.

CHAPTER 8

How do Organisms Reproduce?

DOWNLOAD PDF CHAPTER 8

Questions Page No: 128

1. What is the importance of DNA copying in reproduction?

Solution:

DNA – Deoxyribonucleic acid is the genetic material that is present in the cells of all organisms. DNA carries genetic

information from one generation to the other, and this helps in producing organisms of its own types. DNA copying is a

must for inheriting the traits from parents. Any variations in DNA copying will give rise to origin of new species.

2. Why is the variation beneficial to the species but not necessarily for the individual?

Solution:

The reason why the variation is beneficial to the species rather than individuals is because sometimes the climatic

changes have a drastic effect on the species, which makes their survival difficult. For examples, if the temperature of

the water body increases, there might be certain species of microorganisms which might die. This may result in

disturbance in the environment. So, variation is beneficial to species and not for the individuals.

3. How does binary fission differ from multiple fission?

Solution:

When a single cell divides into two equal halves, it is known as binary fission. Bacteria and amoeba are examples of

binary fission.

When a single cell divides into multiple daughter cells at the same time, it is known as multiple fission. Algae and

sporozoans are examples of multiple fission.

4. How will an organism be benefited if it reproduces through spores?

Solution:

Following are the ways through which an organism will be benefited if it reproduces through spores:

 Number of spores produced in one sporangium would be large.

 In order to avoid competition at one place, spores can be distributed to faraway places with the help of air.

 In order to prevent dehydration under unfavorable conditions, the spores are covered by thick walls.

5. Can you think of reasons why more complex organisms cannot give rise to new individuals through

regeneration?

Solution:

Organisms at higher complex levels cannot give rise to new individuals through regeneration because they have

organization of their organs system at different levels. All these organ systems are interconnected and work in full

coordination. They can regenerate a few of their lost body parts like skin, blood, muscles, etc. but can’t give rise to new

individuals.

6. Why is vegetative propagation practised for growing some types of plants?

Solution:

Following are the advantages of practising vegetative propagation for growing some types of plants:

 Crops like orange, banana, pineapple do not have viable seeds, so vegetative propagation can be used.

 It is a rapid, cheap and easier method to grow crops.

 It can be used in places where seed germination fails.

 A good quality of variety can be preserved.

7. Why is DNA copying an essential part of the process of reproduction?

Solution:

DNA copying is an essential part of the process of reproduction because it carries the genetic information from the

parents to offspring. A copy of DNA is produced through some chemical reactions resulting in two copies of DNA.

Along with the additional cellular structure, DNA copying also takes place, which is then followed by cell division into

two cells.

Questions Page No: 140

1. How is the process of pollination different from fertilization?

Solution:

Pollination is defined as the process of transfer of pollens from anther to stigma. The process takes place with the help

of pollinators like air, water and some insects.

Fertilization is defined as the fusion of male and female gametes. It takes place in the ovule and leads to the formation

of zygote.

2. What is the role of the seminal vesicles and the prostate gland?

Solution:

Lubrication of sperms and providing of a fluid medium for the easy transportation of sperms takes place with the help

of secretions from the seminal vesicles and the prostate gland. These secretions also provide nutrients in the form of

fructose, calcium and some enzymes.

3. What are the changes seen in girls at the time of puberty?

Solution:

Following are the changes seen in girls at the time of puberty:

 Hair growth appears in genital area.

 Hair growth in other areas like underarms, face, hands and legs.

 The size of uterus and ovary increases.

 The size of the breast increases followed by darkening of the nipple skin that is present at the tip of the breast.

 Beginning of menstrual cycle.

 Appearance of pimples, as there is more oil secretion from the skin.

4. How does the embryo get nourishment inside the mother’s body?

Solution:

The lining of the uterus thickens after fertilization. The blood flow is good so as to nourish the growing embryo.

Placenta is a special tissue which is embedded in the uterine wall and helps the embryo get the nourishment from the

mother’s tissue. Placenta has villi on the embryo side and blood space on the mother’s side. This spacing provides a

large area between the mother and the embryo and also for waste removal.

5. If a woman is using a Copper-T, will it help in protecting her from sexually transmitted diseases?

Solution:

No, the usage of copper-T cannot stop the contact of body fluids. Hence, it cannot protect her from getting sexually

transmitted diseases.

CHAPTER 9

Heredity and Evolution

DOWNLOAD PDF CHAPTER 9

Exercise 9.1 Page: 143

1. If a trait A exists in 10% of a population of an asexually reproducing species and trait B exists in 60% of the

same population, which trait is likely to have arisen earlier?

Solution:

Trait B is more probable to arise early as this trait has already been existing and replicating in a larger percentage of the

population as compared to trait A.

2. How does the creation of variations in a species promote survival?

Solution:

Genetic variations enable the species to better adapt to changes in its environment. Moreover, it is an important force in

evolution as it allows the frequency of alleles to increase or decrease through natural selection. These variations will

determine the difference between extinction or continuation of the species.

Exercise-9.2 Page: 147

1. How do Mendel’s experiments show that traits may be dominant or recessive?

Solution:

Mendel showed that the traits could either be dominant or recessive through his experiments that focused on the mono-

hybrid cross. The experiment involved him crossing tall (TT) pea plants with dwarf (tt) pea plants. The resultant plants

which formed after fertilisation represented the F1 (or filial) generation. All the F1 plants were tall. Mendel then

proceeded to self-pollinate the filial generation plants, and the result was that 1/4th of the plants obtained in the F2

generation were dwarfs. From this experiment, Mendel concluded that the F1 tall plants were not true-breeding;

instead, they carried the traits for both tall and dwarf heights. A portion of the plants was tall due to the fact that the

traits for tallness were dominant over the traits for dwarfness. This cements the notion that traits can either be dominant

or recessive.

2. How do Mendel’s experiments show that traits are inherited independently?

Solution:

Mendel’s experiments show that traits are inherited independently through his dihybrid cross experiment. The

experiment involved him using two traits – namely, seed shape and seed colour. The colour yellow (YY) is dominant

over green (yy), while the round shape (RR) is dominant over the wrinkled shape (rr). The F2 progeny of the dihybrid

cross resulted in a phenotypic ratio of 9:3:3:1; therefore, 9 plants with round yellow (RRYY) seeds, 3 plants with round

green (RRyy) seeds and 3 plants with wrinkled yellow (rrYY) seeds and one with wrinkled green seeds (rryy). He

further observed that the wrinkled greens and the round yellow are parental combinations while the round green and

wrinkled yellow are new. A dihybrid cross between two seeds with dominant traits (RRYY) and non-dominant traits

(rryy) resulted in the production of 4 types of gametes (RY, Ry, rY and ry). This means each of the gametes segregates

independently of the other, and each with a frequency of 25% of the total gametes produced.

3. A man with blood group A marries a woman with blood group O, and their daughter has blood group O. Is

this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?

Solution:

Given information is not enough to tell us which characteristics are dominant – blood group A or O. Blood type A is

always dominant in ABO blood, and blood type O is always recessive. Here, the father’s blood group may be

genotypically AA (homozygous) or AO (heterozygous), whereas that of the mother can be OA or OO.

4. How is the sex of the child determined in human beings?

Solution:

The sex of the child in humans is determined by the males. Males have XY chromosomes, while females have XX

chromosomes. Hence, if:

 The male’s X chromosomes combine with the female’s X chromosomes, the mother gives birth to a girl

 The male’s Y chromosome combines with the female’s X chromosome, the mother gives birth to a boy

CHAPTER 10

Light-Reflection and Refraction

DOWNLOAD PDF CHAPTER 10

Questions Page: 168

1. Define the principal focus of a concave mirror.

Answer-

Light rays that are parallel to the principal axis of a concave mirror converge at a specific point on its principal axis

after reflecting from the mirror. This point is called the principal focus of the concave mirror.

2. The radius of curvature of a spherical mirror is 20 cm. What is its focal length?

Answer-

Radius of curvature (R) = 20 cm

Radius of curvature of the spherical mirror = 2 × Focal length (f)

R = 2f

f= R/2 = 20 / 2 = 10

Therefore, the focal length of the spherical mirror is 10 cm.

3. Name the mirror that can give an erect and enlarged image of an object.

Answer-

The mirror that can give an erect and enlarged image of an object is a Concave Mirror.

4. Why do we prefer a convex mirror as a rear-view mirror in vehicles?

Answer-

A convex mirror is preferred as a rear-view mirror in cars and vehicles as it gives a wider field of view, which helps the

driver see most of the traffic behind him. Convex mirrors always form an erect, virtual, and diminished image of the

objects placed in front of it.

NCERT Solutions for Class 10 Science Chapter 10

Light Reflection and Refraction

Questions Page No: 176

1. A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away

from the normal? Why?

Answer-

The light ray bends towards the normal. When a light ray enters from an optically rarer medium (which has a low

refractive index) to an optically denser medium (which has a high refractive index), its speed slows down and bends

towards the normal. As water is optically denser than air, a ray of light entering from air into water will bend towards

the normal.

2. Light enters from air to glass, having a refractive index 1.50. What is the speed of light in the glass? The speed

of light in vacuum is 3 x 108

ms-1.

Answer-

Refractive index of a medium (nm) = Speed of light in vacuum/Speed of light in the medium

Speed of light in vacuum (c) = 3 × 108

m/s

Refractive index of glass (ng) = 1.50

Speed of light in the glass (v) = Speed of light in vacuum/ Refractive index of glass

= c/ng

=3 × 108

/1.50 = 2x 108

ms-1.

Search This Blog

Shine study

Quality Sleep: Unlocking the Benefits of a Restful Night for Overall Health