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Page No 373:

Question 1:

Give the name and formula of a substance which on treatment with chlorine yields bleaching powder.


Calcium hydroxide(Ca(OH)2) on treatment with chlorine yields bleaching powder.
Ca(OH)2+Cl2CaOCl2Bleaching powder+H2O

Page No 373:

Question 2:

Refractive index of media A, B, C and D are:

A 1.33
B 1.52
C 1.44
D 1.65
In which of the four media is the speed of light (i) maximum (ii) minimum?


Speed of light decreases when it travels through a denser medium. The density of a medium depends upon the refractive index of the medium. More the refractive index more the density of the medium.

(i) So, in the given case, speed of light would be maximum in medium A, as it has the least refractive index, so least dense as compared to others.

(ii) Speed of light would be minimum in medium D, as it has the highest refractive index, so the densest medium as compared to others.

Page No 373:

Question 3:

Select the biodegradable items from the list given below.
​Polythene bags, old clothes, wilted flowers, pencil shavings, glass bangles, bronze statue, vegetable peels


Biodegradable substances - old clothes, wilted flowers, pencil shavings, vegetable peels

Page No 373:

Question 4:

What is the importance in India of hydropower plants? Describe how electric energy is generated in such plants?


In India, hydropower plants have great importance because they convert the potential energy of the water into electrical energy. In India we have many natural sources of water i.e. water falling from the mountain has more potential energy which can be converted into a large amount of electricity. 

In hydropower plants, there is a turbine which is connected to the generator which produces electricity. When water at some height falls on the turbine, the turbine starts rotating. So, the potential energy of the water converts into mechanical energy. When the turbine rotates, it makes the generator to produce electricity. So, the mechanical energy gets converted into electrical energy.  

Page No 373:

Question 5:

(a) Define (i) oxidation, and (ii) reduction.
(b) Identify the substances oxidised and reduced in the chemical reaction:
MnO2 + 4HCl → MnCl2 ​+ Cl2 + 2H2O  


(i) Oxidation: Addition of oxygen, removal of hydrogen and loss of electrons is known as oxidation.
Reduction: Addition of hydrogen, removal of oxygen and gain of electrons is known as reduction.


MnO2 changes to MnCl2, here Mn loses oxygen, so it is reduction.
HCl changes to Cl2, here Cl loses hydrogen, so it is oxidation.


Page No 373:

Question 6:

An element X has mass number 35 and the number of neutrons in its atom is 18.
(a) To which group of the periodic table  element X belongs?
(b) To which period of the periodic table element X belongs?
​(c) What will be the formula of chloride of element X?


The mass number of element X = 35
Number of neutrons of element X = 18

The mass number of an element equals the total number of protons and neutrons present in it.
Mass number = number of protons + number of neutrons
35=number of protons+18Number of protons=35-18Number of protons=17
And we know, number of protons = number of electrons
So, the number of electrons = 17

(a) Electronic configuration of element X will be 2, 8, 7.
So it belongs to the halogen family, 17 group.

(b) It belongs to 3rd period of the periodic table.

(c) The formula of chloride of element X will be XCl.

Page No 373:

Question 7:

(a) What happens when potassium iodide solution is added to lead nitrate solution? Give equation of the reaction involved. What type of reaction is represented by this example?
​(b) Give one example of another reaction which is of the same type as the above reaction.


(a)When potassium iodide solution is added to lead nitrate solution, it gives potassium nitrate and yellow lead iodide precipitate. This reaction is an example of double displacement reaction or precipitation reaction.


(b) When barium chloride is treated with sodium sulphate, it gives white precipitate of barium sulphate and aqueous sodium chloride.


Page No 373:

Question 8:

(a) Write two equations to show the extraction of copper from its sulphide ore.
​(b) How will you refine copper? Draw a labelled diagram of the electrolytic cell used for the refining of copper.


(i) Concentrated copper sulphide ore is roasted in air, to give oxidized copper oxide.
Then in the absence of air, the copper oxide formed above reacts with the remaining copper sulphide to form copper metal and sulphur dioxide.


Electrolysis of copper is done using copper electrodes. The crude copper serves as the anode while a thin sheet of pure copper serves as the cathode.
At cathode: Cu+2+2e- CuAt anode: Cu Cu+2+ 2e-

As anode dissolves away, the cathodes on which the pure metal is deposited grows in size.

Page No 374:

Question 9:

(a) What are ionic compounds and covalent compounds? Give the name and formula of one ionic compound and one covalent compound.
​(b) Write the major points of difference between ionic compounds and covalent compounds.


(a) Ionic compounds: Ionic compounds are formed by permanent transfer of electrons from one element to another, to achieve the noble gas configuration. For eg. sodium chloride(NaCl), magnesium chloride(MgCl2) etc..
Covalent compounds: Covalent compounds are formed by sharing of electrons. For eg. hydrochloric acid(HCl), methane(CH4) etc..


Covalent compound  Ionic compound
1. They have a characteristic shape. 1. They are generally crystalline solids.
2. They have low melting and boiling point as compared to the ionic compound except for diamond. 2. They have high melting and boiling point due to the strong electrostatic force of attraction.
3. They are bad conductors of electricity except carbon in the form of graphite. 3. They are good conductors of electricity in the molten state.
4. They are soluble in the non-polar solvents or polar solvents. 4. They are soluble in the polar solvent.

Page No 374:

Question 10:

(a) Draw ray diagrams to illustrate the formation of a virtual image by using (i) a convex lens, and (ii) a concave lens.
​(b) What is the difference between the two images formed above?


(a) (i)



(b) The virtual image formed by the convex lens is enlarged but the image formed by the concave lens is smaller than the object.

Page No 374:

Question 11:

(a) What is an electromagnet? Draw a labelled diagram to show the making of a simple electromagnet.
​(b) State three factors on which the strength of an electromagnet depends. How does the strength of electromagnet depend on these factors?


(a) An electromagnet is a device used to generate a magnetic field with the help of an electric current. Unlike permanent magnets, the strength of an electromagnet can be increased by increasing the amount of current flow through them. 

(b) Three factors affecting the strength of an electromagnet are as follows:

(i) Strength of the current passing through the core of the magnet.
(ii) The number of tunes of the wire in the core.
(iii) The material of the core

When the current flowing through the core is increased, the magnetic field produced by the current increases, therefore the strength of the electromagnet increases.

Increase in the number of turns of the wire of core also increases the magnetic field, hence the strength of the electromagnet increases by increasing the number of turns in the wire of the coil.

The metal inside the coil magnifies the field created by it. Changing the metal core for a different metal will make the electromagnet stronger or weaker. 

Page No 374:

Question 12:

(a) What is a nuclear reactor? What is the fuel used in a nuclear reactor?
(b) What type of nuclear reaction is carried out in a nuclear reactor?
(c) How is the working nuclear reactor of a power plant shut down in an emergency?
​(d) Name five places in India where nuclear power plants are located.


(a) A nuclear reactor is a device used to initiate and control a self-sustained nuclear chain reaction. Nuclear reactors are mainly used at nuclear power plants to produce electricity. The fuel used in a nuclear reactor is commonly known as nuclear fuel. The most common nuclear fuels are radioactive metals uranium-235 and plutonium-239.

(b) Nuclear fission reactions are carried out in a nuclear reactor. 

(c) In case of an emergency, the control rods are fully inserted in the reactor. They absorb all the neutrons responsible for the chain reaction, which helps in shutting down the reactor. 

(d) Five places in India where nuclear power plants are located are as follows:

(i) Kudankulam Nuclear Power Plant - Tamil Nadu.
(ii) Tarapur Nuclear Reactor - Maharashtra.
(iii) Rajasthan Atomic Power Plant - Rajasthan. 
(iv) Kaiga Atomic Power Plant - Karnataka.
(v) Narora Nuclear Reactor - Uttar Pradesh.

Page No 374:

Question 13:

(a) How is small intestine designed to absorb the digested food efficiently?
(b) What would be the consequences of a deficiency of haemoglobin in our bodies?
​(c) Why should the forests and wildlife be conserved?


(a) Absorption of food refers to the process of absorption of nutrients derived from the breakdown of food through digestion into the blood. It takes place in small intestine.
The inner walls of the small intestine have thousands of finger-like projections called villi. These structures increase the surface area for absorption of the digested food. Villi contain a network of blood vessels inside the small intestine. The substances absorbed by the villi enter blood vessels and are transported to different organs of the body.

(b) Haemoglobin is present in the red blood cells and transports oxygen to the body cells. Deficiency of haemoglobin in the human body can lead to the deficiency of oxygen in the blood. It can also lead to anaemia.

(c) It is important to conserve the forests and wildlife because they have an important role in maintaining the ecological balance. 

Page No 374:

Question 14:

(a) What are producers, primary consumers, secondary consumers and tertiary consumers? Give one example of each.
​(b) Write a food chain having four trophic levels. Mark the producer and various types of consumers in it.


(a) Producers - Producers are organisms which can produce their own food and are autotrophic in nature. Example: plants
Primary consumers - Primary consumers are herbivores which feed on plants. Example: rabbit
Secondary consumers - Refers to organisms who are carnivores and feed on other animals for their nutrition. Example: snake
Tertiary consumers - Refers to organisms who feed on animals which eat other animals. Example: Hawk

(b) Plant  (Producer) → Grasshopper (Primary consumer) → Frog (Secondary consumer) → Snake (Tertiary consumer) 

Page No 374:

Question 15:

(a) Name the processes of reproduction in the following organisms:
(i) Malarial parasite (Plasmodium)          (ii) Yeast
​(b) Describe the process of reproduction in Hydra with the help of labelled diagrams.


(a) (i) Malarial parasite (Plasmodium) - Multiple fission 
(ii) Yeast - Budding

(b) Hydra reproduces by the process of budding. It involves the formation of a new individual from a protrusion called bud

In Hydra, the cells divide rapidly at a specific site and develop as an outgrowth called bud. These buds, while attached to the parent body, develop into small individuals. When this individual becomes large enough, it detaches itself from the parent body to exist as an independent individual.

Page No 374:

Question 16:

(a) Name the metal which is extracted from haematite ore?
(b) Name one ore of aluminium. Name the aluminium compound present in this ore and write its chemical formula.
(c) How is aluminium metal extracted? Explain with the help of an equation.
(d) Name the electrode at which aluminium metal is produced.
(e) Which gas is produced during the extraction of aluminium? At which electrode is this gas produced?
​(f) What is an alloy? Name two alloys of aluminium.


(a) The metal extracted from hematite ore is iron.

(b) Bauxite is an ore of aluminium. The aluminium compound present in this ore is aluminium oxide. Its chemical formula is Al2O3.2H2O.

(c) Aluminium is extracted by electrolytic reduction of its molten oxide. Aluminium is a highly reactive metal and it is placed at the top of the reactivity series. It cannot be reduced by other reducing agents such as coke, carbon monoxide, etc..
On passing electricity through molten aluminium oxide, decomposition reaction occurs and formation of aluminium metal and oxygen gas takes place.


Molten aluminium oxide consists of aluminium and oxide ions. The reaction that occurs during electrolysis are:
1) Cathode produces electrons to reduce aluminium ions to aluminium atoms by acting as a reducing agent. Aluminium ions are cations, therefore, they get attracted to negatively charged cathode and get deposited there


2) Oxide ions are anions, therefore, they get attracted to the positively charged anode. These oxide ions are oxidized to oxygen gas. Oxygen gas is produced at the anode.


(d) Aluminium metal is produced at the cathode. During electrolysis, cathode produces electrons to reduce aluminium ions into aluminium atoms by acting as a reducing agent. Aluminium ions are cations, therefore, they get attracted to negatively charged cathode and get deposited there.


(e) Oxygen gas is produced during the extraction of aluminium. The oxygen gas is produced at the anode. During electrolysis, aluminium atoms are deposited at cathode, whereas oxide ions, being anions, get attracted to the positively charged anode. These oxide ions are oxidized to oxygen gas. Oxygen gas is produced at the anode.


(f) When a metal is mixed with another element (metal or a non-metal) such that a new substance of homogeneous composition is obtained, the substance obtained is known as an alloy. For eg. Al-Li alloy (lithium), Alnico (aluminium, nickel, copper).

Page No 374:

Question 17:

(a) What is a soap? Name one soap.
(b) Describe the structure of a soap molecule with the help of a diagram.
(c) Explain the cleansing action of soap. Draw diagrams to illustrate your answer.
​(d) Give the main differences between soaps and detergents.


(a) Soaps are sodium and potassium salts of long chain fatty acids containing 12-18 carbon atoms. For eg. sodium salt of stearic acid is sodium stearate (C17H35COONa).

(b) A soap is a sodium or potassium salt of long-chain fatty acids. It has one polar end (the end with the sodium or potassium ion) and one non-polar end (the end with the fatty-acid chain). The polar end is hydrophilic in nature, i.e., this end is attracted towards water. The non-polar end is hydrophobic, but lipophilic in nature, i.e., it is attracted towards hydrocarbons, but not attracted towards water.


Each soap molecule has two ends. These are:
(i) The polar, Ionic hydrophilic end.
(ii) The non-polar, non-ionic hydrophobic end.
Mechanism of cleansing action of soap:
1. Soap gets dissolved in water
2. The non-polar end gets directed towards the center and the polar end gets directed outwards.
3. A cluster compromising of this arrangement is formed which is known as a micelle.
4. The dirty cloth is put in a soap solution.
5. Dust or oil is hydrophobic in nature. The non-polar end gets attached to the oil or dirt present in the cloth and polar end remain attached to water.
6. The dirty cloth is agitated in the solution.
7. Oily and greasy particles entrapped in soap micelle gets dispersed in water.
8. Soap water gets dirty and the cloth gets cleaned.


Soaps Detergents
1. Soaps are the sodium salts of long chain carboxylic acids. 1. Detergents are sodium salts of long-chain benzene sulphonic acids.
2. The ionic group is soaps is COO-Na+. 2. The ionic group in soaps is SO3-Na+ or SO4-Na+
3. Soaps are not useful when water is hard. 3. Detergents can be used for washing purpose even when water is hard.
4. Soaps are biodegradable. 4. Some detergents are non-biodegradable.
5. Soaps have relatively weak cleansing action. 5. Detergents have a strong cleansing action.


Page No 375:

Question 18:

(a) Explain the principle of working of a hydroelectric power plant.
(b) What is tidal energy? How can it be utilized?
(c) State any two uses of solar cells.
(d) Explain why, a solar cooker box is (i) painted black from inside, and (ii) covered with a glass sheet.
​(e) Give two reasons why Biogas is a good domestic fuel.


(a) The principle of hydropower is that the potential energy of the water stored at great heights in the dam is converted into kinetic energy by allowing the water to flow at high speed. The high-speed water then falls on a turbine, which is connected to a generator. The kinetic energy of the water gets converted into mechanical energy, which rotates the shaft of the generator, which further produces electricity and the mechanical energy gets converted into electrical energy. 

(b) Energy due to the movement of the water in areas with high tidal movements is known as tidal energy. Few large underwater turbines are placed in areas with high tidal movements. Then the kinetic energy of the tidal water is used to rotate the turbine, which is connected to a generator to produce electricity. So, tidal energy is mainly used to generate electricity like hydroelectric power plants.

(c) (i) Solar cells are used to make handheld calculators or wrist watches
(ii) Solar cells are used to convert light energy from the sun into electrical energy.

(d) (i) Solar cooker box is painted black so that it can absorb most of the sunlight which falls on it.
(ii) Solar cooker box is covered with a glass sheet so that the absorbed heat from the sunlight can be trapped inside the box and the temperature inside the box can be increased to cook the food.

(e) Biogas is considered as good fuel because of the following reasons:
(i) Biogas does not cause air pollution.
(ii) Biogas produces a large amount of heat per unit mass.

Page No 375:

Question 19:

With the help of a labelled circuit diagram, describe an activity to illustrate the pattern of the magnetic field lines around a straight current carrying long conducting wire.
(a) Name the rule that is used to find the direction of magnetic field associated with a current carrying conductor.
(b) Is there a similar magnetic field produced around a thin beam of moving (i) alpha particles, and (ii) neutrons? Justify your answer.


(a) The direction of the magnetic field associated with a current carrying conductor is determined by the Right-hand thumb rule. According to this rule if we point our thumb in the direction of current then the direction of the fold of our fingers give the direction of the magnetic field around the conductor.

(b) The reason for the magnetic field around a current carrying conductor is the motion of the charged particles or electron inside the conductor.

(i) As alpha particles are positively charged so their movement will also produce a magnetic field.

(ii) Neutrons do not carry any charge so their motion will not produce any kind of magnetic field.

Page No 375:

Question 20:

(a) "Improvements in our lifestyle have resulted in greater amounts of waste generation." Give two examples to support the given statement. Suggest one change that we can incorporate in our lifestyle in order to reduce non-biodegradable waste.
(b) The following organisms form a food chain. Write the food chain.
        Insect, Hawk, Grass, Snake, Frog
Which of these will have highest concentration of non-biodegradable chemicals? Name the phenomenon.


(a) The above statement can be supported by two facts -

  • Recetnly, its been a trend to use disposable materials like cups, plates, spoons etc in marriages and parties. These are usually made up of non biodegradable substances like plastic and styrofoam which eventually result in polluting our environment.
  • Another example is the use of disposable plastic cups in trains. These leads to generation of a lot of plastic waste. However, they are being slowly replaced by paper cups to reduce the burden on the environment.
We should try to minimise the use of disposable/ one time use products in our daily lifes.

(b) The food chain is 

Grass →Insect →Frog →Snake→ Hawk

The highest concentration of non biodegradable chemicals will be present in Hawk as it occupies the last trophic level.

This phenomenon is termed as biomagnification. It is defined as the increase in the concentration of pollutants or harmful chemicals with the increase in trophic level.

Page No 375:

Question 21:

(a) Name the various organs of human excretory system. Draw a labelled diagram of human excretory system. What is the function of excretory system in humans?
​(b) What is meant by dialysis? What type of patients are put on dialysis?


(a) The human excretory system is composed of a pair of kidneys, tube - like structures called ureter, a urinary bladder and a urethra.

Functions of the human excretory system:

• It helps in eliminating unwanted substances like ammonia, urea, uric acids, excess water, etc., from the body.

• It helps in maintaining the water balance of the body.

• It helps in maintaining the normal pH of the blood and other fluids inside the body.

• It helps in eliminating the drugs and toxins that we intake unknowingly.

• It helps in regulating body temperature by releasing sweat.

(b) If the kidneys fail to function, wastes may accumulate in the body, the body may retain excess fluid, and blood pressure may rise. In such a case, an artificial kidney or hemodialysis is useful.
- In hemodialysis, only a few drops of blood are allowed to flow, through a special filter that removes wastes and extra fluid. The detoxified blood is then returned to the body.
- â€‹The special filter used in dialysis consists of a number of tubes with semi-permeable lining, suspended in a tank filled with the dialysis fluid.
It is used for patients with kidney failure.

Page No 375:

Question 22:

You are given following current-time graphs from two different sources:

(a) Name the type of current in two cases.
(b) Identify any one source for each type of these currents.
(c) What is the frequency of current in case II in India?
​(d) Use above graphs to write one difference between the current in two cases.


(a) The current shown in the graph 'I' is a DC(Direct current). Whereas the current shown in graph 'II' is an AC(Alternating current).
(b) An AC generator can be used to produce Alternating current(AC) and Direct current or DC can be produced by batteries or cells.
(c) Frequency of the Alternating current in India is 50 Hz.
(d) The main difference between the current in two cases is that in direct current (DC), the electric charge (current) flows only in one direction. But, in alternating current (AC), on the other hand, the charge flow (current) changes direction periodically. 

Page No 376:

Question 23:

A student is performing an experiment to study the formation of image of a lighted candle by a converging lens. The converging lens has a focal length of 25 cm and the candle is placed at a distance of 15 cm from the lens.
(a) State three characteristics of the image of the candle so formed which will be observed by the student.
​(b) Name a simple device which works under these conditions.


(a) The focal length of the given lens is 25 cm. The object is placed at 15 cm, that means the object lies between the pole and the focus of the lens. The characteristic of the image formed by the convex lens, in this case, are as follows:

(1) The image formed would be erect
(2)The image formed would be virtual.
(3) The image formed would be enlarged

(b) A convex lens is used in a magnifying glass and in simple microscope where we need to see the object enlarged than its normal sizes such as while reading a book or a magazine.

Page No 376:

Question 24:

A small piece of sodium metal is added to a neutral organic liquid, taken in a dry test-tube. Bubbles of a gas are produced in the test-tube. When a burning match-stick is brought near the mouth of the test-tube, the gas burns with a 'pop' sound, making a little explosion.
(a) Name the functional group present in the organic liquid.
​(b) Write the name and formula of an organic liquid having this functional group.


(a) When we treat ethanol with sodium metal, sodium ethoxide is formed and hydrogen gas is released.


So, the functional group present in the organic compound will be alcohol (OH).

(b) Ethanol (C2H5OH) has the functional group alcohol.

Page No 376:

Question 25:

A student was given a white powder and asked to study the action of water on it. When the student added some water to this white powder, it set into a hard mass in about half an hour.
(a) What is the common name and chemical formula of white powder?
​(b) Name its two uses.


(a) The white powder is calcium sulphate hemihydrate(CaSO4.12H2O). Commonly known as plaster of paris.

(b) Uses of plaster of paris:
1. used for the treatment of fractured/broken bones
2. used for making toys, making surfaces smooth and for decoration purposes

Page No 376:

Question 26:

A scientist performed experiments to analyse the two samples of air given to him:
'Air Sample A' and 'Air Sample B'. The results of analysis of these two air samples are given below:

Air Sample A   Air Sample B
Oxygen : 21%   Oxygen : 16.4%
Carbon dioxide : 0.04%   Carbon dioxide : 4.4%
Water vapour : A little   Water Vapour : A lot

(a) Which air sample, A or B, represents 'exhaled air'? Why?
(b) Which air sample, A or B, represents 'inhaled air'? Why?​


Sample B represents exhaled air. 
Exhaled air contains more amount of carbon dioxide and water vapor.

Sample A represents inhaled air.
Inhaled air contains more amount of oxygen and less amount of carbon dioxide and vapor.

Page No 376:

Question 27:

Write the number given to any six of the organisms shown in Figure B against their relevant trophic levels given in Figure A below.


Producer - (8)  Grass
Primary consumers - (7) Rabbit
Secondary consumers - (3) Snake
Tertiary consumers - (4) Vulture

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