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Question 1:

Which one of the following gases is the major constituent of biogas?
  Carbon monoxide, Hydrogen, Methane, Carbon dioxide

Answer:

Out of given gases, methane is the major constituent of biogas.

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Question 2:

Name two inorganic substances which are used by autotrophs to make food.

Answer:

 Two inorganic substances which are used by autotrophs to make food are carbon dioxide and water.

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Question 3:

(a) Dry hydrogen chloride gas does not turn blue litmus red whereas hydrochloric acid does. Give one reason.

(b) An organic compound burns with a sooty flame. Is it a saturated or an unsaturated compound? Give reason.
 

Answer:

(a) Blue litmus is an indicator which changes colour only in the presence of ions like H+ or H3O+.
Hydrochloric acid in its aqueous form dissociates and produces H+ ions which turn the blue litmus red. However, dry hydrogen chloride gas cannot dissociate and produce H+ ions, as a result of which it cannot turn blue litmus red.

(b) An organic compound which burns with a sooty flame will be an unsaturated compound.
Saturated hydrocarbons contain lower percentage of carbon and get completely oxidised in the presence of oxygen.
Whereas unsaturated hydrocarbons contain higher percentage of carbon as a result of which they are not completely oxidized in the presence of oxygen. These unburnt carbon particles produce a lot of smoke and soot.

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Question 4:

An electric geyser has the ratings 2000 W, 220 V marked on it. What should be the minimum rating, in whole number, of a fuse wire that may be required for safe use with this geyser?

Answer:

Power of the geyser = 2000 W

Voltage = 220 V

Maximum current = PowerVoltage=2000 W220 V=9.09 A


The current that passes through the circuit having the geyser is 9.09 Amp. The rating of the fuse must be more than 9.09 A for safe use with this geyser. That's why the required minimum rating should be 10 A.

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Question 5:

What do the following transport?
(i) Xylem      (ii) Phloem      (iii) Pulmonary vein     (iv) Vena cava

Answer:

 (i) Xylem - Water and minerals
(ii) Phloem - Food
(iii) Pulmonary vein - Oxygenated blood
(iv) Vena cava - Deoxygenated blood



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Question 6:

You are given three resistors of 10 Ω, 10 Ω and 20 Ω, a battery of emf 2.5 V, a key, an ammeter and a voltmeter. Draw a circuit diagram showing the correct connections of all given components such that the voltmeter connected across the ends of 20 ​Ω resistor gives a reading of 2.0 V.

Answer:



The ammeter and key are connected in series with the battery and the resistors. We have connected two 10 Ω resistors in parallel and its combination is in series with another 20 Ω resistor. This is because the effective resistance of two 10 Ω resistors, connected in parallel will be 5 Ω and will consume only 0.5 volts from the battery. The remaining 2 volts will be consumed by the 20 Ω resistors. Thus, the voltmeter connected in parallel with it will show a reading of 2 volts.

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Question 7:

A person is able to see objects clearly only when these are lying at distances between 50 cm and 300 cm from his eye.
(a) What kind of defects of vision is he suffering from?
(b) What kind of lenses will be required to increase his range of vision from 25 cm to infinity? Explain briefly.

Answer:

(a) The person is suffering from both Myopia and Hypermetropia. It is because the range of a normal eye vision is from 25 cm to infinity, where 25 cm is the shortest distance for the distinct vision and infinity is the longest distance for the vision of a normal healthy eye. Since the person can only see the objects lying in between 50 cm to 300 cm, therefore he is suffering from both the defects.

(b) The lense required to increase his range of vision from 25 cm to infinity should be a bifocal lens consists of a concave lens for distant vision and convex lens for near vision.   

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Question 8:

What is the meaning of the term 'frequency' of an alternating current? What is its value in India?
Why is an alternating current considered to be advantageous over direct current for long-range transmission of electric energy?

Answer:

The number of times the electric current changes its direction in one second in an ac circuit gives us the frequency of an alternating current. In India, the frequency of the alternating current is 50 kHz.
Alternating current is considered advantageous over direct current because it can be stepped up or stepped down using a transformer which makes it more suitable for transmission of electric power over long distances without loss of energy.

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Question 9:

(a) Differentiate between nuclear fission and nuclear fusion.
(b) Which of the two, nuclear fission or nuclear fusion, is made use of:
(i) for the production of electricity?
(ii) for making a hydrogen bomb?

Answer:

(a) Nuclear fusion is the process where two or more nuclei collide at high speeds and combine to form a stable atomic nucleus whereas nuclear fission is the process of splitting of an unstable atomic nucleus into two lighter and stable nuclei. 

(b) (i) Nuclear fission provides less energy which we are able to control and prevent it from creating too much energy at the same time. That's why nuclear fission is used for the production of electricity. 

(ii) On the other hand, Nuclear fusion releases a lot of energy which we are not yet able to control. Nuclear fusion is no problem when devising destruction itself. So, it is used for making a hydrogen bomb. 

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Question 10:

(a) A metal M forms an oxide having the formula M2O3. It belongs to 3rd period in the modern periodic table. Write the atomic number and valency of the metal.
(b) Write the formula of chloride of metal M.
(c) What could metal M be?

Answer:

(a) Metal M has the formula M2O3, from which it is clear that the
valency of M = +3 
valency of O = -2

Since M is in the third period, its outer most/third shell will have three valence electrons which will give it a configuration as 2, 8, 3.

So, the atomic number of the M = 13

Hence, M will be aluminium and its formula will be Al2O3.

(b) Valency of metal M is +3 so it will form MCl3 type compound with alkaline earth metals. Since M is aluminium, the compound will be AlCl3.

(c)  The atomic number of the M = 13 which means that the metal M will be aluminium.

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Question 11:

Two carbon compounds A and B have the molecular formulae C3H8 and C3H6 respectively. Which one of the two is most likely to show addition reaction? Justify your answer. Explain with the help of a chemical equation, how an addition reaction is useful in vegetable ghee industry.

Answer:

The general formula for the classification of hydrocarbons is given as:
a) Alkanes             CnH2n+2
b) Alkenes             CnH2n

Thus, compound A, C3H8 is an alkane and the compound B, C3H6 is an alkene.
Addition reaction takes place in unsaturated compounds. This reaction will be seen in compound B as it is an unsaturated compound.
For eg.  


Vegetable oils belong to the category of unsaturated compounds as they contain double bonds. They exist as liquids at room temperature. These oils being unsaturated undergo addition reaction to add hydrogen and become saturated. These saturated products are called vegetable ghee or vanaspati ghee and they remain solid at room temperature.

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Question 12:

Write the electron-dot structure for sodium and chlorine atoms. How do these form a chemical bond? Name the type of bond so formed. Why does a compound so formed have high melting point?

Answer:

Electron dot structure: 



Sodium has only one electron in its valence shell while chlorine has seven electrons in its valence shell. So, to achieve a noble gas configuration sodium will lose its electron and chlorine will accept those electrons to complete its octet. Formation of this type of bond is known as an ionic bond.



The ionic bond which is formed between Na and Cl is a strong bond where the Na and Cl atoms are strongly attracted to each other. It requires lot of energy to break this bond due to which they have high melting point.

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Question 13:

(a) What is the function of a flower?
(b) Name those parts of the flower which serve the same function as the following do in the animals:
​(i) testis   (ii) ovary   (iii) eggs   (iv) sperms

Answer:

In plants, flower is the functional unit concerned with the sexual reproduction of plants. It is the most important part in angiosperms because the reproductive parts are located inside it.

(i) Testis : Anther
(ii) Sperm : Pollen grains
(iii) Ovary : Ovary
(iv) Egg : Ova/Ovum

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Question 14:

(a) What is meant by respiration?


(b) A graph was plotted to show the energy output of two types of respiration:

(i) Identify the types of respiration denoted by curves A and B.
(ii) How do you arrive at your answer?

Answer:

(a) Respiration is the process of breakdown of complex C-C bonds of organic compounds which results in the release of considerable amount of energy that can be used by an organism.

(b) (i) Graph B shows aerobic respiration whereas graph A shows anaerobic respiration.
(ii) The energy output in graph B is more as compared to the energy output in graph A. In aerobic respiration, large amounts of energy is produced compared to the anaerobic respiration.



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Question 15:

(a) What is the scientific name of malarial parasite? Name the method of its reproduction.
(b) Write one feature which is common to each of the following pairs of terms/organs.
(i) glycogen and starch    (ii) chlorophyll and haemoglobin
​(iii) gills and lungs          (iv) arteries and veins

Answer:

 (a) Malaria is caused by the parasite Plasmodium. There are four different species of this parasite which cause malaria. Plasmodium reproduces by multiple fission.

(b) (i) glycogen and starch - carbohydrates
(ii) chlorophyll and haemoglobin - pigments
(iii) gills and lungs - respiratory sructures
(iv) arteries and veins - blood vessels

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Question 16:

An organic compound 'A' is widely used as a preservative in pickles and has a molecular formula C2H4O2. This compound reacts with ethanol to form a sweet smelling compound 'B'.
(i) Identify the compound 'A'.
(ii) Write the chemical equation for its reaction with ethanol to form compound 'B'.
(iii) How can we get compound 'A' back from 'B'?
(iv) Name the process and write corresponding chemical equation.
(v) Which gas is produced when compound 'A' reacts with washing soda? Write the chemical equation.

Answer:

(i) An organic compound A widely used as a preservative in a pickle with the molecular formula, C2H4O2 must be an ethanoic acid (CH3COOH).

(ii) When ethanoic acid(A) reacts with ethanol it produces sweet-smelling compound i.e. an ester.
CH3COOH+CH3CH2OHCH3COOCH2CH3+H2O
Hence, the compound B will be ethyl ethanoate.

(iii) We can get ethanoic acid from ethyl ethanoate by hydrolysis in either acidic or basic medium.
CH3COOCH2CH3+H2OH+CH3COOH+CH3CH2OHCH3COOC2H5+NaOHCH3COONa+C2H5OH

(iv) The hydrolysis of ester in the presence of base is generally known as saponification.
CH3COOC2H5+NaOHCH3COONa+C2H5OH

(v) When compound A is treated with washing soda brisk effervescence of carbon dioxide is observed.
 2CH3COOH+Na2CO32CH3COONa+CO2+H2O
 

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Question 17:

You are given the following materials:
(i) Iron nails
(ii) Copper sulphate solution
(iii) Barium chloride solution
(iv) Copper powder
(v) Ferrous sulphate crystals
(vi) Quicklime

Identify the type of chemical reaction taking place when:
(a) Barium chloride solution is mixed with copper sulphate solution and a white precipitate is observed.
(b) On heating copper powder in air in a china dish, the surface of copper powder turns black.
(c) On heating green coloured ferrous sulphate crystals, reddish brown solid is left and smell of a gas having odour of burning sulphur is experienced.
(d) Iron nails when left dipped in blue colour copper sulphate solution become brownish in colour and the blue colour of copper sulphate fades away.
(e) Quick lime reacts vigorously with water releasing a large amount of heat.
Write chemical equations for each one of the above reactions.

Answer:

(a) When barium chloride solution is mixed with the copper sulphate solution, we get barium sulphate as the precipitate. The reaction is precipitation reaction or double displacement reaction.
BaCl2(aq)+CuSO4(aq)BaSO4(s)+CuCl2(aq)

(b) When copper oxide is heated, it combines with oxygen in the air to form copper oxide. This copper oxide is black in colour, because of which the surface of copper powder turns black. This reaction is a redox reaction.
Cu(s)+O2(g)2CuO

(c) Ferrous sulphate is green in colour. On being heated, it loses water of crystallization and is converted to anhydrous ferrous sulphate. The anhydrous ferrous sulphate on further heating decomposes to ferric oxide, sulphur dioxide and sulphur trioxide. Ferric oxide is reddish brown in colour. This is an example of a decomposition reaction.
 2FeSO4FeO+SO2+SO3

(d) When iron nails are dipped in copper sulphate solution, then the blue colour of solution will slowly fade away also a brown substance will be deposited on the iron nail. This substance is nothing but copper metal. This reaction takes place because iron is more reactive than copper and is placed above it in the reactivity series. Hence, iron displaces copper from copper sulphate and instead forms FeSO4 and copper metal. It is a displacement reaction.
CuSO4(aq)+Fe(s)FeSO4(aq)+Cu(s)

(e) When quick lime is added to water, then calcium hydroxide is formed. A large amount of heat is released in the process. This reaction is a combination reaction.
CaO(s)+H2O(l)Ca(OH)2(aq)

 

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Question 18:

(a) Draw ray diagrams to show the formation of a three times magnified (i) real image (ii) virtual image, of an object kept in front of a converging lens. Mark the positions of object, F, 2F, O and position of image clearly in the diagram.
(b) An object of size 5 cm is kept at a distance of 25 cm from the optical centre of a converging lens of focal length 10 cm. Calculate the distance of the image from the lens and size of the image.

Answer:

18 (a)

(i)
 

(ii) 



18(b) Focal length of the lens, f = 10 cm

The distance of the object from the lens, u = 25 cm

Height of the object, ho = 5 cm

Using lens formula, 1f=1v-1u

110=1v-1251v=110+125=750v=507 cm

Magnification,

m=vu=hiho507×25=hi5hi=107 cm

Hence, the distance of the image from the lens is 507cm and the size of the image is 107cm.

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Question 19:

Give reasons for the following:
(i) The sky appears to be blue during day time to a person on earth.
(ii) The sky near the horizon appears to have a reddish hue at the time of sunset and sunrise.
(iii) The sky appears dark instead of blue to an astronaut.
(iv) The stars appear to twinkle.
​(v) The planets do not twinkle.

Answer:

(i) The scattered light's color depends on the size of the scattering particles. The particles of very small size scatter mainly blue light whereas, the particles of larger size scatter lights of longer wavelengths. The sky appears blue because the fine particles present in the earth's atmosphere scatter blue light the most among all the components of white light.

(ii) At sunrise or sunset, the Sun is located near the horizon. So, the light has to travel a long distance through the Earth’s atmosphere. At the time of sunrise or sunset, when white sunlight falls on suspended atmospheric particles, the blue color light scatters out in the atmosphere, while the red color light scatters less and reaches the eyes of the observer on the surface of the Earth. Hence, when this less scattered red light reaches the eyes of the observer, the Sun and its surroundings appear reddish.

(iii) The sky appears dark instead of blue to an astronaut because there is no atmosphere in the outer space that can scatter the sunlight. As the sunlight is not scattered, the sky appears black to them.

(iv) The light coming from the stars undergoes refraction through the earth’s atmosphere. The physical conditions of the earth’s atmosphere keep changing. As a result of that, the path and also the amount of refracted starlight changes continuously through the atmosphere. Therefore, the stars sometimes appear brighter and sometimes fainter. As a result of this, the stars appear to be twinkling.

(v) Planets are closer to the earth and thus are extended sources of light. In the case of planets, the amount of light entering our eyes is significantly large. Even if the physical conditions of the earth’s atmosphere keep changing, the total variation in the amount of light entering our eyes is negligible. Therefore, the amount of light coming from the planets does not change with slight variations in atmospheric conditions. Therefore, planets do not twinkle.
 



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Question 20:

(a) What are hormones? Give some of the characteristics of hormones?
(b) Which hormone is released into blood when its sugar level rises? Name the organ which produces the hormone and its effect on blood sugar level. Also name one digestive enzyme that this organ secretes and the function of this enzyme.

Answer:

(a) Hormones are intercellular chemical messengers secreted by specific endocrine glands of the body, which travel through the body to reach target organs or cells and initiate a process. Chemically, hormones are proteins. Once the hormone is secreted from the gland, it is directly poured into the blood stream, which transports it to the site of action. They maintain the balance of biological activities in the body.

Characteristics of hormones:

(i) act as chemical messengers

(ii) secreted by endocrine glands

(iii) act upon specific cells/tissues/organs called target cells/tissues/organs

(iv) either accelerate or inhibit a reaction

(b) Insulin is released into the blood when sugar level rises. Pancreas produce insulin which controls the amount of sugar by converting glucose into glycogen. It does not act on the glucose directly but causes cells to convert glucose into glycogen.
Pancreas also produce pancreatic juice, which contains several enzymes. One such enzyme is trypsinogen (proenzyme). The activated trypsin converts the proteases and peptones into dipeptides.

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Question 21:

(a) Quote three instances where human intervention saved the forests from destruction.
(b) Explain that it is a matter of chance whether a couple will give birth to a boy or a girl. Draw the necessary diagram to illustrate your answer.

Answer:

(a) Three instances  where human intervention saved the forests from destruction are -

  • Chipko Andolan (Hug the Trees Movement):
This movement originated in a remote village called Reni, in Garhwal, in the early 1970s. A contractor was given permission to cut down the trees in a forest near the village. However, the villagers were against the decision. They were aware that diminishing forest cover would disturb the ecological balance. Therefore, there was a dispute between the contractor and the villagers. On a particular day, when the men folk of the village were away at work, the employees of the contractor visited the forest to cut down the trees. The women of the village then reached the forest, and each one wrapped her hands around a tree trunk, thereby preventing the workers from destroying the forest.
  • Arabari forest range of Midnapore district, West Bengal:

Another example of active participation of people towards the conservation of biodiversity is found in an incident related to the Arabari forest range in Midnapore district, West Bengal. A forest officer, A. K. Banerjee, involved the villagers for the protection of the 1272 hectares of badly degraded Sal forests. In return, the villagers were provided with employment opportunities in silviculture and harvesting. They were also allowed to collect firewood from the forest. The effect of this involvement was that the forest became dense and green within a period of 10 years.

  • Another example is the association of Bhishnois of Rajasthan

In 1971, Bishnois in Rajasthan gave up their lives while trying to prevent the king’s men from cutting trees.


(b) In human beings, the females have two X chromosomes and the males have one X and one Y chromosome. Therefore, the females are XX and the males are XY.

At the time of mating, large number of sperms is ejaculated from the male reproductive organ (penis), into the female reproductive organ i.e. vagina. They travel towards the fallopian tubes, where only one sperm meets with the egg.

The process of fusion of sperm and ovum is called fertilization. The sperm has either X or Y chromosome and egg has only X chromosome. So, if a sperm carrying Y chromosome fuses with the egg, the newly born child will be male and if a sperm carrying X chromosome fuses with the egg the newly born child will be female.

There is equal chance of fusion of either X or Y chromosome with the egg so we can say that the sex of new born child is a matter of chance and none of the parent is responsible for it.

Sex determination in human is shown below:

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Question 22:

Draw the pattern of magnetic field lines of a current carrying solenoid. What does the pattern of field lines inside the solenoid indicate? Write one application of magnetic field of current carrying solenoid.

Answer:



The field lines inside the solenoid are in the form of parallel straight lines. Which indicates that the magnetic field is the same at all points inside the solenoid. i.e. the field is uniform inside the solenoid. The magnetic field of a current carrying solenoid is used in making electromagnets.

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Question 23:

A ray of light AM is incident on a spherical mirror as shown in the diagram.



​Redraw the diagram on the answer sheet and show the path of the reflected ray. Also, indicate and mark the angle of reflection in the diagram.

Answer:



When a light ray parallel to the principal axis falls on a concave mirror, it reflects and passes through the focus of the mirror as shown in the figure.

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Question 24:

A student dropped few pieces of marble in dilute hydrochloric acid contained in a test tube. The evolved gas was passed through lime water. What change would be observed in lime water? Write balanced chemical equations for both the changes observed

Answer:

Marble is chemically calcium carbonate (chemical formula CaCO3). When a few pieces of marble are dropped in dilute hydrochloric acid, the two compounds react to form calcium chloride, carbon dioxide, and water.
CaCO3+2HClCaCl2+CO2+H2O

Thus, the brisk effervescence observed is due to the formation of carbon dioxide gas. When carbon dioxide gas is passed through lime water, it turns lime water milky due to the formation of calcium carbonate.
Ca(OH)2+CO2CaCO3+H2O

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Question 25:

A housewife wanted her house to be whitewashed. She bought 10 kg of quicklime from the market and dissolved it in 30 litres of water. On adding quicklime to water she noticed that the water started boiling even when it was not being heated. Give reason for her observation. Write the corresponding chemical equation and name the product formed.

Answer:

Quick lime is chemically calcium oxide (CaO). When quick lime is added to water, calcium hydroxide is formed. This reaction is highly exothermic i.e. a large amount of heat is released in this process. This is why when quick lime is added to water it starts to boil even without heating.

CaO(s)+H2O(l)Ca(OH)2(aq)

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Question 26:

The given experimental set up tests the responses of different parts of plant towards gravity. Use scientific terms for the conclusions.

Answer:

The response of shoot to sunlight i.e. bending of shoot in the direction of sunlight is called phototropism.
The response of root to gravity i.e. growth of roots in the downward direction is called geotropism.

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Question 27:

A student was viewing a leaf peel under a microscope. He observed green, dot-like structures in some cells.
(a) What are the green, dot-like structures?
​(b) What is this green colour due to?

Answer:

(a) These green dot like structures are called chloroplasts.
(b) The green colour is due to the presence of photosynthetic pigment chlorophyll.



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