CBSE Previous Year Question Papers Class 10 Science 2017 Outside Delhi Term 2
Time allowed: 3 hours
Maximum marks: 80
- The question paper comprises five sections, A, B, C, D and E. You are to attempt all the sections.
- All questions are compulsory.
- Internal choice is given in Sections B, C, D and E.
- Questions number 1 and 2 in Section A are one mark questions. They are to be answered in one word or in one sentence.
- Questions number 3 to 5 in Section B are two marks questions. These are to be answered in about 30 words each.
- Questions number 6 to 15 in Section C are three-marks questions. These are to be answered in about 50 words each.
- Questions number 16 to 21 in Section D are five-marks questions. These are to be answered in about 70 words each.
- Questions number 22 to 27 in Section E are based on practical skills. Each question is a two marks question. These are to be answered in brief.
CBSE Previous Year Question Papers Class 10 Science 2017 Outside Delhi Term 2 Set I
Section – A
Write the molecular formula of the 2nd and the 3rd member of the homologous series whose first member is methane. 
Ethane – C2H6
Propane – C3H8
When a cell reproduces, what happens to its DNA? 
During the process of reproduction, the transmission of DNA from parents to offspring takes place. Before reproduction, DNA is replicated, which means two copies of DNA are produced. When the cell divides, the two copies are distributed equally between the two daughter cells so that a similar amount and type of DNA is transferred from the parent cell to the daughter cells. It maintains the consistency in the amount and type of DNA in the living organism of a particular species.
In the following food chain, 100J of energy is available to the lion. How much energy was available to the producer? 
Plant → Dear → Lion
Plant → Dear → Lion
According to 10% law,
10% of x = 100
x = 1000 J in deer.
10% of y = 1000
y = 10,000 J in Plant.
An object is placed at a distance of 30 cm from a concave lens of focal length 15 cm. List four characteristics (nature, position, etc.) of the image formed by the lens. 
Given: u = -30 cm, f = -15 cm. (for concave lens)
We know that,
Characteristics of image:
- The image is formed at a distance of 10 cm from the concave lens on the left side.
- Image formed is virtual.
- Image formed is erect.
- The size of the image formed is diminished.
State two advantages of conserving
(i) forests, and
(ii) wildlife. 
(i) Advantages of conserving forest:
- It supports life, purifies air.
- Holds the soils and thus prevents the soil erosion.
(ii) Advantage of conserving wildlife:
- Balances ecology and biodiversity.
- Provides important things to sustain life.
Explain two main advantages associated with water harvesting at the community level. 
Two advantages associated with water harvesting at community level are:
- Water harvesting is an ideal solution to water problems in areas having inadequate water resources.
- It improves the quality of water and helps in raising the groundwater level.
Write the structural formula of ethanol. What happens when it is heated with excess of cone. H2SO4 at 443 K? Write the chemical equation for the reaction stating the role of cone. H2SO4 in this reaction. 
Structural formula of ethanol is:
When ethanol is heated with excess of conc. H2SO4 at 443K it results in the dehydration of ethanol to give ethene.
Role of conc. H2SO4: Conc. H2SO4 acts as a dehydrating agent which removes water from the ethanol.
Distinguish between esterification and saponification reaction with the help of the chemical equations for each. State one use of each (i) esters, and (ii) saponification process. 
Esterification is opposite of saponification. In esterification:
RCOOH + R’OH → RCOOR’ + H2O
Whereas in saponification:
RCOOR’ + NaOH → RCOONa + R’OH
(i) Uses of Esters : Esters are used in making perfumes.
(ii) Uses of saponification reaction: Used in making soaps and soap products on a large scale.
Write the number of periods and groups in the Modem Periodic Table. How does the metallic character of elements vary on moving
(i) from left to right in a period, and
(ii) down a group ? Give reason to justify your answer. 
In the modem periodic table, there are 18 vertical columns known as Groups and 7 horizontal rows known as Periods.
Metallic character: It is defined as the tendency of an atom to lose electrons.
(i) Across the period i.e., from left to right, metallic character decreases.
(ii) Down the group i.e., from top to bottom, metallic character increases.
Reason: Across the period, the effective nuclear charge increases, thus decreasing its atomic radius. This favours the electronegativity and therefore the tendency ‘ to lose electrons is low. This accounts for the decrease in the metallic character. As we move down the group, the number of shells keep on increasing and therefore the atomic size increases and electronegativity decreases. This enhances the ability to lose electrons and therefore the metallic character increases.
Na, Mg and Al are the elements of the 3rd period of the Modern Periodic Table having group number 1, 2 and 13 respectively. Which one of these elements has the (a) highest valency, (b) largest atomic radius, and (c) maximum chemical reactivity ? Justify your answer stating the reason for each. 
Sodium (Na), At. number 11, 2, 8, 1
Magnesium (Mg), At. number 12, 2, 8, 2
Aluminium (Al), At. number 13, 2, 8, 3
(a) The element having the highest valency is Al, as it has 3 valence electrons.
(b) The element with the largest atomic radius is Na as left to right atomic radius decreases.
(c) The element with maximum chemical reactivity is Na as metallic character decreases left to right.
Reproduction is one of the most important characteristics of living beings. Give three reasons in support of the statement. 
Reproduction is an energy-consuming process which is not essential for the survival of an individual. But it is highly essential for all the living beings because of the following reasons:
- Reproduction helps in increasing the number of members of a population.
- By replacing the dead members with the new ones, it minimizes the risk of extinction of a species.
- It brings about variations in species, thus, leading to their evolution.
What is vegetative propagation ? State two advantages and two disadvantages of this method. 
Vegetative propagation is a mode of asexual reproduction in which new plants are obtained from vegetative parts of the plants such as shoots or stem for the propagation of new plants.
Two advantages of vegetative propagation are:
- Plants which do not produce seeds are propagated by this method.
- Vegetative propagation is a cheaper, easier and rapid method of propagation in plants than growing plants from their seeds. Plants grow very slowly and take 4 to 7 years to develop flowers when grown with their seeds.
Two disadvantages of vegetative propagation are:
- As there is no genetic variation, there is no chance of development of new and better varieties.
- The vegetatively propagated plants are more prone to diseases that are specific to the species.
List three techniques that have been developed to prevent pregnancy. Which one of these techniques is not meant for males ? How does the use of these techniques have a direct impact on the health and prosperity of a family? 
Three techniques that have been developed to prevent pregnancy are:
- Mechanical Methods: Include condoms, diaphragm, IUCDs, etc.
- Chemical Methods : Include oral contraceptive pills, spermicide.
- Surgical Method: Includes vasectomy and tubectomy.
The chemical methods are not meant for males.
The use of such contraceptive methods have various benefits, such as:
- Large size of families have a negative impact on the economic status of the family.
- Having pregnancies at quick successions reduces mother’s health and vitality. Use of contraceptive devices thus, effects the maternal health status.
- Some contraceptive devices (such as condoms) are also helpful in preventing sexually transmitted diseases.
How did Mendel explain.that it is possible that a trait is inherited but not expressed in an organism? 
Some traits that are inherited may not express themselves. Such hidden traits are known as recessive traits. Mendel explained this phenomenon with the help of monohybrid cross. In a monohybrid cross performed by Mendel, tall plant was crossed with a dwarf plant which produced all tall plants in F1 progeny.
However, when these F1 tall plants were crossed with each other, both tall and dwarf pea plants were obtained in F2 generation. Reappearance of the dwarf pea plants in F2 generation proves that the dwarf trait was inherited but not expressed in F1 generation.
So, dwarfness traits of plants (pea plant) were not lost but are suppressed in the F1 generation and thus reappears in F2 generation.
“Evolution and classification of organisms are interlinked”. Give reasons to justify this statement. 
Classification refers to the grouping and naming of organisms based on the similarities and difference in their characters. Classification is done on the basis of ancestral characteristics and derived characteristics. So as we move from simple life forms to the complex organisms, we are actually tracing the path of evolution. All life forms on earth have progressively changed during evolution. So the hierarchy develops during classification which throws the light on the evolutionary relationship among organisms. Common ancestors can also be predicted with the help of classification.
If the image formed by a lens for all positions of an object placed in front of it is always erect and diminished, what is the nature of this lens? Draw a ray diagram to justify your answer. If the numerical value of the power of this lens is 10 D, what is its focal length in the Cartesian system ? 
It is a concave lens (diverging lens).
State the cause of dispersion of white light by a glass prism. How did Newton, using two identical glass prisms show that white light is made of seven colours ? Draw a ray diagram to show the path of a narrow beam of white light, through a combination of two identical prisms arranged together in inverted position with respect to each other, when it is allowed to fall obliquely on one of the faces of the first prism of the combination. 
When a beam of white light enters a prism, it gets refracted at point and splits into its seven constituent colours. This splitting of the white light occurs because of different angles of bending for each colour and this different angles of bending occurs because different components of light have different refractive indices when passing through the glass prism.
Firstly, Newton made white light to fall on a prism, this cause dispersion of white light into seven colours. Newton then placed an inverted prism in the path of a colour band of seven colours. Only a beam of white ‘ light comes out from the second prism. So, Newton concluded that white light comprises of seven component colours.
(a) Water is an elixir of life, a very important natural resource. Your science teacher wants you to prepare a plan for a formative assessment activity, “How to save water, the vital natural resource”. Write any two ways that you will suggest to bring awareness in your neighbourhood, on how to save water.
(b) Name and explain any one way by which the underground water table does not go down further. 
(a) Water is one of the most precious natural resources that has varied importance in our lives. It is an essential component of the human body, and is used almost everywhere in our day to day activities such as cooking, washing, farming etc. It is an indispensable part of our lives, without which life on earth is not possible. However, the amount of freshwater available for sustaining life is very less, so it is very important to save water by the following ways:
- Turning off the taps during brushing, washing clothes/utensils etc., and use of buckets instead of showers for bathing.
- Reusing of water by storing water after washing fruits and vegetables for watering plants and cleaning cars.
(b) The underground water table can be recharged through rainwater harvesting. Rainwater harvesting is a process by which rain water is collected and stored for the purpose of recharging the ground water or for future use like for irrigation and agriculture. In India, rainwater harvesting is an old tradition which is followed till now in many parts of India. For example, bawris are traditional architectual rainwater harvesters that were built for collecting water in the state of Rajasthan.
There are two ways of rainwater harvesting:
- Surface run off harvesting: In urban areas, rainwater that flows away from the surface can be collected and used for various purposes.
- Rooftop rainwater harvesting: The rainwater on the roofs of the buildings is collected through canals that drains the water into ground reservoirs. This stored water is later utilised.
Why are certain compounds called hydrocarbons? Write the general formula for homologous series of alkanes, alkenes and alkynes and also draw the structure of the first member of each series. Write the name of the reaction that converts alkenes into alkanes and also write a chemical equation to show the necessary conditions for the reaction to occur. 
Compounds consisting of carbon and hydrogen are known as hydrocarbons.
1. Saturated hydrocarbons: Alkanes (CnH2n+2) are the compounds of carbon which have single bond.
2. Unsaturated hydrocarbons: The compounds of carbon having double bonds are alkene (CnH2n) and those having triple bonds are alkyne (CnH2n-2).
The reaction which converts unsaturated hydrocarbons to saturated hydrocarbons i.e., alkenes to alkane is known as hydrogenation reaction. It is used to obtain ghee from oil.
(a) Write the functions of each of the following parts in a human female reproductive system:
(iii) Fallopian tube
(b) Write the structure and functions of the placenta in a human female. 
(a) (i) Functions of the Ovary:
- It produces female gametes (ova).
- It secretes female sex hormones
(ii) Functions of Uterus:
- It supports and nourishes the developing foetus.
- It expands according to the growth of the baby.
(iii) Functions of Fallopian tubes:
- They carry eggs from the ovary to the uterus.
- They act as the site for fertilisation.
(b) The placenta is the connecting link between the mother’s body and the baby. It is a disc embedded in the uterine wall. This special tissue contains villi on the embryo’s side of the tissue. The mother’s end of the placenta has blood spaces, which surrounds the villi. Placenta functions as a site of exchange of materials between the blood of the mother to the baby. The developing embryo generates certain waste substances that are also removed through placenta. Thus, the placenta serves as the nutritive, respiratory and excretory organ of the foetus.
With the help of one example for each, distinguish between the acquired traits and the inherited traits. Why are the traits/ experiences acquired during the entire lifetime of an individual not inherited in the next generation? Explain the reason for this fact with an example. 
|S.No.||Acquired traits||Inherited traits|
|1.||Those traits that are developed by the individual during his lifetime.||Those traits which are present in an individual since birth.|
|2.||They are a result of changes in non-reproductive issues.||They are a result of changes in the DNA.|
|3.||They cannot be passed on to the progeny, e.g., pierced ear, large muscle size etc.||They are transmitted in the progeny, e.g., colour of eyes, skin or hair.|
Traits can be passed on to the next generation only when they have some direct effect on the genes. The traits acquired during the lifetime of an individual cannot be inherited as they do not affect the genetic makeup of an organism. In fact, these traits develop due to the use and disuse of organs or due to the direct effect of the environment. Thus, they are not passed on to the next generation. For example, a wrestler develops large muscles because of his training programme, it does not mean that his offspring will necessarily have large muscles. Similarly, if a lady pierces her nose, the children produced to her will not have pierced nose by birth.
Analyse the following observation table showing a variation of image-distance (v) with object-distance (u) in case of a convex lens and answer the questions that follow without doing any calculations:
|Object-Distance u (cm)||Image-Distance v (cm)|
(a) What is the focal length of the convex lens ? Give a reason to justify your answer.
(b) Write the serial number of the observation which is not correct. On what basis have you arrived at this conclusion?
(c) Select an appropriate scale and draw a ray diagram for the observation at S. No. 2. Also, find the approximate value of magnification. 
(a) From observation 3, the radius of curvature of the lens is 40 cm as distance of object and the distance of the image is same.
Focal length, f = = = 20 cm.
(b) S. No. 6 is not correct, as for this observation the object distance is between focus and pole and in such cases, the image formed is always virtual, but in this case real image is forming as the image distance is positive, hence, v should be negative
(a) If the image formed by a mirror for all positions of the object placed in front of it is always diminished, erect and virtual, state the type of the mirror and also draw a ray diagram to justify your answer. Write one use such mirrors are put to and why.
(b) Define the radius of curvature of spherical mirrors. Find the nature and focal length of a spherical mirror whose radius of curvature is + 24 cm. 
(a) The type of the mirror is a convex mirror. (diverging mirror)
The ray diagram is shown below:
Use of convex mirror: Convex mirror is used as rearview mirror in vehicles as it always produces a virtual, erect and diminished image of an object. So, images of vehicles over a wide area can be seen easily in it.
(b) Radius of curvature: The distance between the centre of curvature and pole of a spherical mirror is called radius of curvature.
R = +24 cm
f = = = +12 cm
The mirror is convex mirror.
(a) A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain
(i) Why the student is unable to see distinctly the objects placed beyond 5 m from his eyes.
(ii) The type of the corrective lens used to restore proper vision and how this defect is corrected by the use of this lens.
(b) If, in this case, the numerical value of the focal length of the corrective lens is 5 m, find the power of the lens as per the new Cartesian sign convention. 
(a) Two possible reasons due to which this defect of vision may have arisen are:
1. Increase in curvature of the lens.
2. Elongation of the eyeball.
(i) A myopic eye has its far point nearer than infinity. It forms the image of a distant object in front of the retina as shown below:
Image is formed in front of Retina
In the given case, student’s far point is 5 m. So, image of the object placed beyond 5 m from his eyes is formed in front of the retina and object appears blurred. That is why the student is unable to see distinctly the objects placed beyond 5 m from his eye.
(ii) Since a concave lens has an ability to diverge the incoming rays. Therefore, it is used to correct this defect of vision. The image is formed at the retina by the use of a concave lens of suitable power as shown.
Section – B
When you add a few drops of acetic acid to a test-tube containing sodium bicarbonate powder, which one of the following is your observation? 
(a) No reaction takes place.
(b) A colourless gas with the pungent smell is released with brisk effervescence.
(c) A brown coloured gas is released with brisk effervescence.
(d) Formation of bubbles of a colourless and odourless gas.
(d) Formation of bubbles of a colourless and odourless gas.
While studying the saponification reaction, what do you observe when you mix an equal amount of colourless vegetable oil and 20% aqueous solution of NaOH in a beaker? 
(a) The colour of the mixture has become dark brown.
(b) A brisk effervescence is taking place in the beaker.
(c) The outer surface of the beaker has become hot.
(d) The outer surface of the beaker has become cold.
(c) The outer surface of the beaker has become hot.
A student requires hard water for an experiment in his laboratory which is not available in the neighbouring area. In the laboratory, there are some salts, which when dissolved in distilled water can convert it into hard water. Select from the following groups of salts, a group, each salt of which when dissolved in distilled water will make it hard. 
(a) Sodium chloride, Potassium chloride
(b) Sodium sulphate, Potassium sulphate
(c) Sodium sulphate, Calcium sulphate
(d) Calcium sulphate, Calcium chloride
(d) Calcium sulphate, Calcium chloride
To perform an experiment to identify the different parts of an embryo of a dicot seed, first of all you require a dicot seed. Select dicot seeds from the following group. 
Wheat, Gram, Maize, Pea, Barley, Groundnut
(a) Wheat, Gram and Pea
(b) Gram, Pea and Ground-nut
(c) Maize, Pea and Barley
(d) Gram, Maize and Ground-nut
(b) Gram, Pea and Ground-nut
The following vegetables are kept in a basket:
Potato, Tomato, Radish, Brinjal, Carrot, Bottle-gourd
Which two of these vegetables correctly represent the homologous structures? 
(a) Carrot and Tomato
(b) Potato and Brinjal
(c) Radish and Carrot
(d) Radish and Bottle-gourd
(c) Radish and Carrot
Study the given ray diagrams and select the correct statement from the following: 
(a) Device X is a concave mirror and device Y is a convex lens, whose focal lengths are 20 cm and 25 cm respectively.
(b) Device X is a convex lens and device Y is a concave mirror, whose focal lengths are 10 cm and 25 cm respectively.
(c) Device X is a concave lens and device Y is a convex mirror, whose focal lengths are 20 cm and 25 cm respectively.
(d) Device X is a convex lens arid device Y is a concave mirror, whose focal lengths are 20 cm and 25 cm respectively.
(d) Device X is a convex lens and device Y is a concave mirror, whose focal lengths are 20 cm and 25 cm respectively.
A student obtains a blurred image of a distant object on a screen using a convex lens. To obtain a distinct image on the screen he should move the lens. 
(a) away from the screen
(b) towards the screen
(c) to a position very far away from the screen.
(d) either towards or away from the screen depending upon the position of the object.
(d) either towards or away from the screen depending upon the position of the object.
A student very cautiously traces the path of a ray through a glass slab for different values of the angle of incidence (∠i). He then measures the corresponding values of the angle of refraction (∠r) and the angle of emergence (∠e) for every value of the angle of incidence. On analysing these measurements of angles, his conclusion would be: 
(a) ∠i > ∠r > ∠e
(b) ∠i = ∠e > ∠r
(c) ∠i < ∠r < ∠e
(d) ∠i = ∠e < ∠r
(b) ∠i = ∠e > ∠r
Study the following ray diagram
In this diagram, the angle of incidence, the angle of emergence and the angle of deviation respectively have been represented by 
(a) y, p, z
(b) x, q, z
(c) p, y, z
(d) p, z, y
(c) p, y, z
Mention the essential material (chemicals) to prepare soap in the laboratory. Describe in brief the test of determining the nature (acidic/alkaline) of the reaction mixture of saponification reaction. 
The essential chemicals required to prepare soap in the laboratory are oil and sodium hydroxide solution. In order to determine the nature of the reaction mixture of saponification reaction, we dip red litmus paper into it which will turn blue after a while indicating that it is a basic mixture.
Draw in sequence (showing the four stages), the process of binary fission in Amoeba. 
Binary Fission in Amoeba is the asexual type of reproduction in which the organism splits directly into two equal¬sized offsprings, each with a copy of the parent’s genetic material.
A student focuses the image of a candle flame, placed at about 2 m from a convex lens of focal length 10 cm, on a screen. After that, he moves gradually the flame towards the lens and each time focuses its image on the screen. 
- In which direction does he move the lens to focus the flame on the screen?
- What happens to the size of the image of the flame formed on the screen?
- What difference is seen in the intensity (brightness) of the image of the flame on the screen?
- What is seen on the screen when the flame is very close (at about 5 cm) to the lens?
- He moves the lens away from the screen to focus on the image.
- Size of the image increases.
- The intensity of the image decreases as the flame moves towards the lens.
- Nothing can be seen as the image formed is virtual.
CBSE Previous Year Question Papers Class 10 Science 2017 Outside Delhi Term 2 Set II
Note: Except for the following questions, all the remaining questions have been asked in the previous set.
Write the molecular formula of the 2nd and 3rd member of the homologous series whose first member is ethene. 
1. Propene: C3H6
2. Butene: C4H8
Newly formed DNA copies may not be identical at times. Give one reason. 
During the process of replication of DNA, most of the base sequences in the new copies are identical to those in the parent DNA. However, some changes can occur either due to mutation or due to minor errors during the replication process. Thus, the newly formed DNA copies may not be identical at times.
In the following food chain, plants provide 500 J of energy to rats. How much energy will be available to hawks from snakes?
Plants → Rats → Snakes → Hawks 
500 J of energy is available to the rats thus according to 10% law, 50 J energy will be available to snakes and 5 J energy will be available to hawk.
An object is placed at a distance of 15 cm from a convex lens of focal length 20 cm. List four characteristics (nature, position, etc.) of the image formed by the lens. 
Given, u = -15 cm, f = 20 cm
v = -60 cm
Four characteristics of the image formed by the lens are:
- At a distance of 60 cm on the same side of the lens as the object
- Enlarged or magnified image.
Why is an equitable distribution of resources essential in a society? List two forces which are against such distribution. 
Equitable distribution of resources is when every individual gets an equal right to access all the available resources and is benefited directly or indirectly. It also avoids the division of society to an extent.
The main forces which work against equitable distribution:
- Lack of natural resources.
- Excessive consumption by the rich.
- Profit motive of people exploiting resources.
- Corruption. (Any two)
Why must we conserve our forests? List two factors responsible for causing deforestation. 
We must conserve forests because we derive countless benefits such as food, timber etc. from them and they are an important component of our ecosystem. Factors that contribute to deforestation are as follows:
- Large scale development projects have contributed to the loss of forests.
- Forests are cleared on a large scale to meet the growing needs of industrialisation, especially fuelwood and for other forest products and minerals.
- Mining has also contributed to deforestation.
- With the increase in population and growing demand for commercial crops and the need for more and more land for agriculture, has to lead to deforestation.
- Growing urbanisation, trees are cut to establish cities, to lay down infrastructure.
What happens when (write a chemical equation in each case)
(a) ethanol is burnt in air?
(b) ethanol is heated with excess cone. H2SO4 at 443 K?
(c) a piece of sodium is dropped into ethanol? 
Explain esterification reaction with the help of a chemical equation. Describe an activity to show esterification. 
The reaction of carboxylic acid with alcohol forms an ester. This process of formation of ester is called esterification.
CH3COOH + CH3CH2OH → CH3COOCH2CH3 + H2O
- Take 1 ml of ethanol and 1 ml of glacial acetic acid in a boiling tube and mix the contents well.
- Add few drops of conc. H2SO4 to it.
- Warm the contents on a water bath for a few minutes.
- Now pour the solution in a beaker containing 20-50 mL of water.
- A sweet fruity smell indicating the formation of an ester is observed.
With the help of two suitable examples, explain why certain experiences and traits earned by people during their lifetime are not passed on to their next generations. When can such traits be passed on? 
The experiences and qualifications that a person earns during their lifetime are examples of acquired traits. These traits are not inherited, they do riot affect the genetic makeup. They are developed due to the direct affect of the environment. Thus they are not passed to the next generation. Piercing of ears or large sized muscles of the wrestler are not carried by the next generation. Traits can only be passed on to the next generation only when they have some direct effect on the genes. For example, mutation is caused in the germ cells of a person due to exposure to some harmful radiations, it is likely that the mutation will be passed on to the subsequent generations.
Describe reproduction by spores in Rhizopus. 
Rhizopus is a fungus that reproduces by spore formation. The fungal hyphae gives rise to a globular structure known as sporangium. The sporangium gives rise to several spores by repetitive division of its nucleus. Each nucleus gets surrounded by a part of cytoplasm and thus develops into a spore. These spores then mature inside the sporangium. Once they are fully mature, the sporangium bursts to release these spores in the environment. Since the spores disperse through air, they can land on various sites. These sites may be favourable or unfavourable. During unfavourable conditions, these spores are protected by a tough coat. Once favourable conditions return, they germinate and grow into new hyphae.
Draw ray diagrams to show the formation of three times magnified (a) real, and (b) virtual image of an object by a converging lens. Mark the positions of O, F and 2F in each diagram. 
(a) For real image: To get a three-times magnified image, the object is placed between F1 & 2F1
(b) For virtual image: To get a three-times magnified image, the object is placed between the F1 and optical centre O.
What is the dispersion of white light? State its cause. Draw a ray diagram to show the dispersion of white light by a glass prism. 
The phenomenon of splitting of white light into its seven constituent colours, when it passes through a glass prism, is called the dispersion of light.
When a beam of white light enters a prism, it gets refracted at point and splits into its seven constituent colours i.e.r violet, indigo, blue, green, yellow, orange and red i.e., VIBGYOR. This splitting of light rays occurs because of the different angles of bending for each colour and this different angles of bending occurs because different components of light have different refractive indices or speed of different colours is different in glass when passing through the glass prism. When a beam of sunlight is allowed to fall on one of the rectangular surfaces of the glass prism, we obtain a coloured spectrum with red and violet colour at its extremes.
CBSE Previous Year Question Papers Class 10 Science 2017 Outside Delhi Term 2 Set III
Note: Except for the following questions, all the remaining questions have been asked in previous sets.
Write the molecular formula of the 2nd and 3rd member of the homologous series where the first member is ethyne. 
1. CH3C = CH (propyne), n = 3
2. CH3CH2C = CH (Butyne), n = 4
Why is variation important for a species? 
Variation is necessary for the survival of species as variation makes species more adapted to survive with the change environmental conditions. The vari? t species are more adapted to changing the environment. Therefore, they can survive better and reproduce to pass the genes to the offsprings.
In the following food chain, 20,000 J of energy was available to the plants. How much energy would be available to man in this chain?
Plants → Sheep → Man 
In the given food chain, according to 10% law,
Plants(20,000J) → Sheep(2000J) → Man(200J)
Amount of energy available to the man is 200 J.
You being an environmentalist are interested in contributing to the conservation of natural resources. List four activities that you can do on your own. 
We can bring the following activities in practice to conserve the natural resources:
- We can reuse and recycle the paper products so that cutting of trees could be reduced.
- We can reduce the consumption of water by avoiding its wastage in our day to day activities.
- We can also adopt water harvesting like rainwater harvesting.
- We can reduce the consumption of fossil fuels by using public transport, carpool and switching off vehicles at signals.
Why are coal and petroleum categorised as natural resources ? Give a reason as to why they should be used judiciously. 
Natural resources are those living and non-living sources available in our environment which are exploited to meet the human requirements. Since coal and petroleum are actually the fossils of the dead plants and animals respectively, hence considered as natural resources.
Both coal and petroleum are used as important sources of energy since long time. Both these fossil fuels were formed millions of years ago from the degradation of biomass. Since these fossil fuels are non-renewable in nature and they have limited reserves, therefore they must be used judiciously, otherwise they will get exhausted very soon.
What is periodicity in properties of elements with reference to the Modem Periodic Table? Why do all the elements of the same group have similar properties? How does the tendency of elements to gain electrons change as we move from left to right in a period ? State the reason of this change. 
The occurence of the elements with similar properties after certain regular intervals when they are arranged in increasing order of atomic number is called periodicity. The periodic repetition of the properties is due to the recurrence of similar valence shell configuration after regular interval.
The elements in a group have same valence electrons thus similar chemical properties. In a period, tendency to gain electrons increases from left to right. This tendency increases because the hold of nucleus on the outermost electrons becomes weak thus it becomes easy to eject the electron.
Write the electronic configuration of two elements X and Y whose atomic numbers are 20 and 17 respectively. Write the molecular formula of the compound formed when element X reacts with element Y. Draw electron-dot structure of the product and also state the nature of the bond formed between both the elements. 
X = 20; 2, 8, 8, 2
Y = 17; 2, 8, 7
The nature of bond will be ionic.
What is an organic evolution ? It cannot be equated with progress. Explain with the help of a suitable example. 
Organic evolution refers to the gradual changes that occur in living organisms over time. It is the result of change in the genetic makeup of the organism due to mutation and other sources of variations. „ The favourable mutations are accepted by nature and provide the organism an adaptive advantage, leading to its evolution. Evolution cannot always be equated to progress because it does not always lead to the formation of a new species. In fact, most of the times, it leads to the generation of diversity. One species does not necessarily get eliminated to give rise to a new ones in prevailing environments. Also, the newly formed species may have complex organisation because of evolution but it cannot be considered better than the earlier species. Many older and simpler designs still survive in the nature. For example, bacteria are one of the simplest life forms on earth and still they can survive in the most adverse conditions, such as hot springs, deep sea thermal vents etc. Therefore, having more complex body designs does not make any species superior to others.
List the two types of reproduction. Which one of the two is responsible for bringing in more variations in its progeny and how? 
Reproduction methods are of two types: Sexual and Asexual. Out of these, sexual reproduction brings more variation in organisms. In sexual reproduction fusion of male and female gametes from different organisms occurs. Since the fusion of gametes come from two different individuals, the offsprings exhibit more diversity of characters. Also during gamete formation, meiosis occurs which brings new combinations of genes. Both these factors lead to more variations in the progeny.
“A lens can form a magnified erect image as well as magnified inverted image of an object placed in front of it.” State the nature of this lens and draw ray diagrams to justify the above statement. Mark the positions of O, F and 2F in the diagram.
Two ray diagrams are drawn to show it-
(a) When object is placed between O and F1, the image formed is magnified, Virtual and erect.
(b) When object is placed between F and 2F, the image formed is magnified and inverted.
What is “dispersion of white light”? Draw a labelled diagram to illustrate the recombination of the spectrum of white light. Why is it essential that the two prisms used for the purpose should be identical and placed in an inverted position with respect to each other? 
The phenomenon of splitting of white light into its constituent colours on passing through a prism is known as the dispersion of white light. This splitting of the light rays occurs because of the different angles of bending for each colour and this different angles of bending occurs because different component of light faces different refractive index (or speed of different colours is different) when passing through the glass prism.
It is essential that the two prisms used for the purpose should be identical and placed in an inverted position with respect to each other so that the second prism completely nullifies the dispersion caused by the first prism and we get pure white light.