CBSE Previous Year Question Papers Class 10 Science SA2 Outside Delhi – 2012

CBSE Previous Year Question Papers Class 10 Science SA2 Outside Delhi – 2012

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Time allowed: 3 hours                                                                                           Maximum marks: 90

GENERAL INSTRUCTIONS:

1.  The Question Paper comprises of two Sections, A and B. You are to attempt both the Sections.
2. All questions are compulsory.
3. All questions ofSection-A and all questions ofSection-B are to be attempted separately.
4. Question numbers 1 to 3 in Section-A are one mark questions. These are to be answered in one word or in one sentence.
5. Question numbers 4 to 6 in Section-A are two marks questions. These are to be answered in about 30 words each.
6. Question numbers 7 to 18 in Section-A are three marks questions. These are to be answered in
   about 50 words each.
7. Question numbers 19 to 24 in Section-A are five marks questions. These are to be answered in about 70 words each.
8.  Question numbers 25 to 36 in Section-B are questions based on practical skills. Question nos. 25 to 33 are MCQs. Each question is a one mark question. You are to select one most appropriate response out of the four provided to you. Question nos. 34 to 36 are short answer questions carrying two marks each.

SET I

SECTION A
Question.1 Write the name and formula of the second member of the carbon compounds having functional group—OH.
Answer. Second member of alcohol family — C₂H₅OH CH₃-CH₂-OH Ethanol

Question.2 State one function of iris in human eye.
Answer. Function of iris. Iris regulates the amount of light entering the eye by adjusting the size of the pupil.

Question.3 What happens when higher energy ultraviolet radiations act on the oxygen at the higher level of the atmosphere?
Answer. The high energy ultraviolet radiation (UV radiation) coming from the Sun splits oxygen
gas into free oxygen atoms

The free oxygen atoms thus produced react with an oxygen molecule to form ozone molecule

Question.4 In a food chain, if 10,000 joules of energy is available to the producer, how much energy will be available to the secondary consumer to transfer it to the tertiary consumer?
Answer.

Question.5 Choose from the following:

Answer.

Question.6 An element ‘X’ belongs to 3rd period and group 17 of the periodic table. State its
(i) electronic configuration, (ii) valency. Justify your answer with reasoning.
Answer.

Question.7(a) State the role of placenta in the development of embryo.
(b) What happens when the egg is not fertilised?
Answer.
(a) Role of placenta. After implantation, a disc like special tissue develops between the uterus wall and the embryo called placenta.
The exchange of nutrients, oxygen and waste products between the embryo and the mother takes place through the placenta.
(b) If the egg does not get fertilised (due to non-availability of sperms in the female body) then the thick and soft inner lining of uterus along with the blood vessels and the dead egg comes out of the vagina in the form of bleeding called menstruation.

Question.8 To construct ray diagram we use two light rays which are so chosen that it is easy to know their directions after reflection from the mirror. List these two rays and state the path of these rays after reflection. Use these rays to locate the image of an object placed between centre of curvature and focus of a concave mirror.
Answer. Rays used and their path after reflection:
(i) A ray parallel to the principal axis after reflection this ray will pass through the principal focus in case of a concave mirror or appear to diverge from the principal focus in case of a convex mirror.
(ii)A ray passing through the centre of curvature of a concave mirror or directed in the direction of the centre of curvature of a convex mirror, after reflection, is reflected back along the same path.

Question.9 (a) Draw a labelled ray diagram to illustrate the dispersion of a narrow beam of white light when it passes through a glass prism.
(b) A star appears slightly higher (above) than its actual position in the sky. Illustrate it with the help of a labelled diagram.
Answer.

Question.10 A 4 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 24 cm. The distance of the object from the lens is 16 cm. Find the position, size and nature of the image formed, using the lens formula.
Answer.

Question.11 List three problems which arise due to construction of big dams. Suggest a solution for these problems.
Answer. Three problems that arise due to construction of big dams:

1. Social problems. Due to the construction of high rise dams, a large number of human settlements are submerged in the water of large reservoir formed by the dam and many people are rendered homeless.
2.  Environmental problems. The construction of high rise dams on the rivers contributes to deforestation and loss of biodiversity.
3.  Economic problems. Some people believe that the construction of high-rise dams involve the spending of huge amounts of public money without the generation of proportionate benefits.
   Suggestions for these problems. All the people who are displaced from the dam site should be given adequate compensation by the Government for rehabilitation so as to start their life afresh.

Question.12 List the products pf combustion of fossil fuels. What are their adverse effects on the environment?
Answer. When fossil fuels are burnt, the products of combustion are—carbon dioxide, water, sulphur dioxide and nitrogen oxides. If combustion takes place in an insufficient supply of air then carbon monoxide is produced. All these products are harmful and create some adverse effects on the environment.

1.  Sulphur dioxide dissolves in rainwater making it acidic. The acid rain thus produced damages trees, plants, buildings and metal structures.
2. Nitrogen oxide also causes acid rain.
3.  Carbon monoxide is a green house gas which traps Sun’s heat energy falling on the earth. The increased carbon dioxide in the atmosphere causes increased green house effects leading to global warming.

Question.13 What is meant by homologous series of organic compounds? Write the chemical formulae of two members of a homologous series and state which part determines the

1.  physical properties,
2. chemical properties, of these compounds.

Answer. A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by CH₂ group. Example: The general formula of. the homologous series of alkenes is where n is
the number of carbon atoms.
1st member is CH₄, 2nd member is C₂H₆

1. The members of a homologous series show a gradual change in their physical pro¬perties with increase in molecular mass, e.g., as the number of carbon atoms increases, the melting points, boiling points and densities of its members increase gradually.
2. All the compounds of homologous series show similar chemical properties because the basic structure of all the members of a homologous series is similar.

Question.14 Na, Mg and A1 are the elements having one, two and three valence electrons , . respectively. Which of these elements

1. has the largest atomic radius,
2.  is least

reactive? Justify your answer stating reason for each.
Answer. Na, Mg and AI are the elements of same period where Na is the first, Mg is the second and A1 is the third member.

1.  Na has the largest atomic radius because on moving from left to right in a period, the atomic radius of elements decreases. As we move from left to right in a period, the atomic number of elements increases and the extra electrons are added to the same
   shell. Due to large positive charge on the nucleus, the electrons are pulled in more close to the nucleus and the size of the atom decreases.
2.  Sodium is very reactive, Mg is less reactive whereas Al is still less reactive because on moving from left to right in a period, the chemical reactivity first decreases and then increases.

Question.15 List and explain in brief three methods of contraception.
Answer. Three different methods of contraception:

1.  Barrier methods. In these methods, physical devices such as condoms, diaphragm and cervical caps are used. These devices prevent the entry of sperm in the female genital tract, thus acting as a barrier between them.
2. Surgical methods. There are surgeries that can be carried out in males and females. In males, a small portion of the sperm duct (vas deferens) is blocked by surgical operation. It prevents the egg to reach the uterus. In both the cases, fertilisation will not take place.
3.  Chemical methods. This category of contraceptives acts by changing the hormonal balance of the body so that eggs are not released and fertilisation cannot occur. Females use two types of pills for preventing pregnancies, i.e., oral pills and vaginal pills. The oral pills contain hormones which stop the ovaries from releasing ovum into fallopian tube. This is also called oral contraceptives (OC).
   Other contraceptive devices such as loop or the copper-T are placed in the uterus to prevent pregnancy.

Question.16 If we cross pure-bred tall (dominant) pea plant with pure-bred dwarf (recessive) pea plant we will get pea plants of  F₁ generation. If we now self-cross the pea plant of F₁ generation, then we obtain pea plants of  F₂ generation.
(a) What do the plants of F₁ generation look like?
(b) State the ratio of tall plants to dwarf plants in F₂ generation.
(c) State the type of plants not found in  F₁, generation but appeared in  F₂ generation, mentioning the reason for the same.
Answer.
(a) The plants of F₁generation are all Tall.
(b) Tall plants : Dwarf plants — 3:1
(c) Dwarf plants: This is because irt  F₂ generation, Tall is a dominant trait whereas in  F₂ generation, two copies of ‘tt’/recessive traits made the plant dwarf.

Question.17 List in tabular form two distinguishing features between acquired traits and inherited traits, with one example of each.
Answer.

Question.18 How are fossils formed? Describe, in brief, two methods of determining the age of fossils.
Answer. When organisms (plants or animals) die, their bodies will decompose by the action of micro-organisms in the presence of oxygen, moisture, etc.
Sometimes in the lack of such conditions (oxygen, moisture, etc.), their body does not decompose completely and is preserved as fossil with the passage of time in the rocks. In many cases the soft parts of the organism get decomposed and hard parts (like bones etc.) become fossil. Sometimes even the soft parts (like leaf etc.) remain preserved as fossils in the form of their impressions inside the rocks.
Methods to determine the age of fossils:

1.  Relative method. The fossils which we find in layers closer to the surface of the earth are more recent; the fossils which are found in deeper layers are older.
2.  Carbon dating. Fossils were once living objects and all living objects contain some carbon-14 atoms which are radio-active. When a living object dies and forms fossil, its carbon-14 radioactivity goes on decreasing gradually. The age of the fossil is found by comparing the carbon-14 radioactivity left in the fossil with the carbon-14 radio¬activity present in the living objects today.

Question.19 Ethanol is one of the most important industrial chemicals. It is used in medicine, to synthesize many important compounds, it is an excellent solvent.
However, inspite of its benefits it causes many social problems. If a person drinks alcohol regularly, he becomes an alcoholic. Alcohol is non-toxic but it produces physiological effects disturbing brain activity. These persons are also a threat to the lives of othets.
(a) Give three reasons in favour and three reasons against ‘alcohol-free world’.
(b) ‘Alcohol drinking should not be potrayed on media.’ Give valid reasons to justify.
(c) As a student what initiative would you take in the concern of “We should condemn
drinking alcohol”.
Answer. (a) In favour of ‘Alcohol-free world’:

•  Alcohol drinking,Jowers inhibitions which leads to increased violence and crime in the
  society.
•  A liver disease ‘cirrhosis’ caused by alcohol can lead to death.
•  Drunken driving leads to increased road accidents.
  Against ‘Alcohol-free world’:
•  Alcohol is used for making some medicines like cough syrups, tincture iodine, some tonics etc.
• Mixed with petrol, it is now being used as a fuel for light vehicles.
•  It is used-for making antifreeze material for cooling engines of vehicles.

(b) ‘Alcohol drinking should not be portrayed on media’ because young people and children are very much influenced by the media.
(c) Initiatives taken by a student to create awareness about drinking alcohol could be:

1. By slogan writing
2.  By debates
3. By article writing
4. By role plays/skits

Question.20 With the help of a ray diagram, state what is meant by refraction of light. State Snell’s law for refraction of light and also express it mathematically.
The refractive index of air with respect to glass is 2/3 and the refractive index of water with respect to air is 4/3. If the speed of light in glass is 2×10⁸ m/s, find the speed of light in (a) air, (b) water.
Answer. Refraction of light. The bending of light when it passes from one medium to another is called refraction of light.

Question.21 List the new Cartesian sign convention for reflection of light by spherical mirrors. Apply these conventions for calculating the focal length and nature of a spherical mirror which forms a 1/3 times magnified virtual image of an object placed 18 cm in front of it.
Answer.

Question.22 What are hydrocarbons? Write the name and general formula of
(i) saturated hydro-carbons,
(ii) unsaturated hydrocarbons, and draw the structure of one hydrocarbon of each type. How can an unsaturated hydrocarbon be made saturated?
Answer.


Or
What are detergents chemically? List two merits and two demerits of using’detergents for cleansing. State the reason for the suitability of detergents for washing, even in the case of water having calcium and magnesium ions.
Answer. Detergents are generally ammonium of sulphonate salts of long chain carboxylic acids.
A detergent is the sodium salt of a long chain benzene sulphonic acid. A common detergent is sodium n-dodecyl benzene sulphonate.
Detergent can lather well even in hard water because they do not form insoluble calcium water. A detergent works by making the oil and grease particles of dirty clothes dissolve in water through the formation of miscelles.
Merits of using detergents. Detergents are strong cleansing agents. Detergents form foam even with hard water.
Demerits of using detergents. Detergents are non-biodegradable.

Question.23 Distinguish between unisexual and bisexual flowers giving one example of each. Draw a diagram showing the process of germination of pollen grains on stigma and label the following parts:
(i) Female germ cell; (ii) Male germ cell; (iii) Ovary
Answer.Difference between unisexual and bisexual flowers

Question.24 Draw a diagram of human female reproductive system and label the part
(i) that produces eggs.
(ii) where fusion of egg and sperm takes place.
(iii) where zygote is implanted.
What happens to human egg when it is not fertilised?
Answer.

SECTION B
Question.25 The aqueous solutions of copper sulphate and zinc sulphate appear
(A) blue and green respectively (B) green and colourless respectively
(C) blue and brown respectively (D) blue and colourless respectively
Answer.(D) blue and colourless respectively

Question.26 On adding acetic acid to sodium hydrogen carbonate in a test tube, a student observes
(A) no reaction
(B) a colourless gas with pungent smell
(C) bubbles of a colourless and odourless gas
(D) a strong smell of vinegar
Answer.(C) bubbles of a colourless and odourless gas

Question.27 Which one of the following are the correct observations about acetic acid?
(A) It hums blue litmus red and smells like vinegar
(B) It hums blue litmus red and smells like burning sulphur
(C) It turns red litmus blue and smells like vinegar
(D) It turns red litmus blue and has a fruity smell
Answer.(A) It hums blue litmus red and smells like vinegar

Question.28 A student has to determine the focal length of a concave mirror by obtaining the image of a distant object on a screen. For getting the best result he should focus
(A) a distant tree or an electric pole
(B) a well-illuminated distant building
(C) well-lit grills of the nearest window
(D) a burning candle placed at the distant edge of the laboratory table
Answer.(A) a distant tree or an electric pole

Question.29 If you are to determine the focal length of a convex lens, you should have ,
(A) a convex lens and a screen
(B) a convex lens and a lens holder
(C) a lens holder, a screen holder and a scale
(D) a convex lens, a screen holder for them and a scale.
Answer.(D) a convex lens, a screen holder for them and a scale.

Question.30 Four students showed the following traces of the path of a ray of light passing through
a rectangular glass slab.

Answer.  (C) III

Question.31 The following figures illustrate binary fission in Amoeba in an incorrect sequence.

Answer. (A) III, II, IV, I

Question.32 A student weighed some raisins and recorded the weight as V. She then soaked the raisins in distilled water. After about 2 hours she removed the raisins, wiped them dry and weighed again and recorded that as ‘y’. The percentage of water absorbed by raisins may be determined using the relationship

Answer.

Question.33 A chain of yeast cells forms because
(A) yeast cells do not separate after budding
(B) daughter cells are unable to survive without parent cells
(C) buds reproduce as soons as they are formed
(D) daughter cells stick together with the help of mucus
Answer. (A) yeast cells do not separate after budding

Question.34 What are cotyledons? How are the number of cotyledons different in gram seed and the maize (com) seed?
Answer. Cotyledons are special structures in the seeds of the plants. Cotyledons store food for the embryo of the plant.
In gram seeds, there are two cotyledons and in maize (com) seeds, there is only one cotyledon.

Question.35 Why is emergent ray parallel to the incident ray, after the refraction of Incident ray through a glass slab?
Answer. ∠i =∠e in this case, and these are alternate angles. So incident ray is parallel to the emergent ray.

Question.36 When boilers of water are used for a very long time, then white layers get deposited on inside of these boilers? How can these white layers be removed? 
Answer. When hard water is used in these bioilers, then white scum of salts present in the hard water gets deposited inside the boilers making a white layer. These white layers can be removed by washing the boilers with dil. HCl acid.

SET II

Except for the following questions, all the remaining questions have been asked in Set-1.
SECTION A
Question.1 Write the name and formula of the first member of the carbon compounds having functional group—COOH.
Answer. First member of carboxylic acid group is:
HCOOH — Methanoic acid.

Question.2 State one function of pupil in human eye.
Answer. The amount of light entering the eye cap be controlled by the pupil. If the intensity of outside light is low, then the pupil expands to allow more light to enter the eye. Gn the other hand, if outside intensity of light is high, then the pupil contracts so that less light enters the eye.

Question.3 State one harmful effect of depletion of ozone layer on the living organisms of the ecosystem.
Answer. If the ozone layer in the atmosphere depletes then the extremely harmful ultraviolet radiations coming from the Sim would reach the earth. These uv-radiations would cause skin cancer and other ailments in men, animals and plants.

Question.4 “DNA copies generated during reproduction will be similar but may not be identical to the original.” Justify the statement.
Answer. A basic event in reproduction is the creation of a DNA copy. This is necessary to produce organisms which are similar to their parents. DNA copying is accompanied by the creation of an additional cellular apparatus. When two DNA copies separate, each with its own cellular apparatus by cellular division, so from one cell, two cells are produced. The process of copying of DNA brings some variations each time. Thus the surviving cells are similar to but subtly different from each other. This inbuilt tendency for variation during reproduction brings variations among the individuals of the same species.

Question.5 The formula of magnesium oxide is MgO. State the formula of barium nitrate and barium sulphate, if barium belongs to the same group as magnesium.
Answer.

Question.6 Choose from the following:

(i) An element having two shells completely filled with electrons.
(ii) Two elements belonging to the same group of the periodic table.
Answer.

(i) Ne has two completely filled shells.
(ii)Li and Na belong to the same group as both have same number of valence
electrons (1).

Question.8 (a) Which two criteria did Mendeleev use to classify the elements in his periodic table?
(b) Which element of period ‘3’ of the modem periodic table

1.  is the most reactive non-metal?
2. is the most reactive metal?
3.  forms ion with -2 charge?
4. forms ion with +2 charge?

Answer.
(a) Mendeleev was guided by two factors:

1. increasing atomic masses.
2. grouping together of elements having similar properties.

(b)

1.  Cl is the most reactive non-metal.
2.  Na is the most reactive metal.
3.  S forms -2 charged ion.
4. Mg forms +2 charged ion.

Question.10 Define the term, dispersion of white light. State the colour which bends

1.  the least,
2.  the most, while passing through a glass prism. Draw the dispersion of light through prism.
   

Answer. Dispersion of white light. The splitting up of white light into seven colours on passing through a transparent medium like a glass prism is called dispersion of white light.

1.  The red colour is deviated the least.
2. the violet colour is deviated the most.

Question.14 “The father is responsible for the sex of a child, not the mother.” Justify this statement.
Answer.

1.  A male has one X-chromosome and one Y-chromosome. Thus half the male gametes have
   X-chromosomes and the other half have Y-chromosomes.
2.  A female has two X-chromosomes. Thus all female gametes have only X- chromosomes.
3. If a sperm carrying Y-chromosome fertilises an ovum carrying X-chromosome, then the child bom will be a boy.
4.  If a sperm carrying X-chromosome fertilises an ovum carrying X-chromosome, then the child bom will be a girl.
   
   Therefore it is the sperm from the father which determines the sex of the child.

Question.17 (a) How are the following related?
(i) Number of valence electrons of different elements in the same group.
(ii) Number of shells of elements in the same period.
(b) How do the following change?
(i) Number of shells of elements as we go down a group.
(ii) Number of valence electrons of elements on moving from left to right in a period.
(iii)Atomic radius in moving from left to right along a period.
(iv)Atomic size down a group.
Answer. (a)
(i)

•  All the elements of a group of the periodic table have the same number of
  valence electrons.
• Group number of an element upto 2 Valance Electrons (VE). is equal to the number of valence electrons and group number of an element having Valance Electrons (VE) more than 2 is equal to (10 + V.E.).

(ii)

•  All the elements of a period of the periodic table have same number of shells.
• The period number of an element is equal to the number of electron shells in its atom.

(b)

1. As we go down in a group, a new shell of electrons is added to the atoms at
   every step.
2.  On moving from left to right in a period, the number of valence electrons increases from 1 to 8.
3. On moving from left to right in a period the atomic radius of elements decreases due to the large positive charge on the nucleus, the electrons are pulled in more close to the nucleus.
4. On going down in a group, the size of the atoms increases as a new shell of electrons is added to the atoms at every step.

Question.18 A 2.4 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 18 cm. The distance of the object from the lens is 12 cm. Find the position, size and nature of the image formed, using the lens formula.
Answer.

SET III

Except for the following questions, all the remaining questions have been asked in Set-I and
Set-11.
SECTION A
Question.1 Write the name and formula of the first member of the carbon compounds having functional group—CHO.
Answer. First member of Aldehyde group (-CHO) is:
Methanal/Formaldehyde, HCOOH.

Question.2 State one role of ciliary muscles in the human eye.
Answer. The focal length of eye-lens can be changed by changing its shape by the action of ciliary muscles.

Question.3 Write the name and formula of a molecule made up of three atoms of oxygen.
Answer. A molecule made up of these atoms of oxygen is:
O₄ –> Ozone

Question.4 What is the colour of the clear sky during day-time? Give reason for it.
Answer. During day time the colour of the sky is blue.
Reason: The molecules of air and other fine particles in the atmosphere have a size smaller than the wavelength of visible light. So these particles scatter more effectively the light
rays of shorter wavelength at the blue end than light of longer wavelengths at the red end. When the scattered blue light enters our eyes, it gives us the feeling of a blue sky.

Question.5 Why do all the elements of the (a) same group have similar properties, (b) same period have different properties?
Answer.
(a) All the members of the same group have similar properties because the elements of a group of same valence electrons.
(b) All the members of the same period have different properties because the elements of a period have different valence electrons.

Question.6 An element E has following electronic configuration:

(a) To which group of the periodic table does element E belong?
(b) To which period of the periodic table does element E belong?
(c) State the number of valence electrons present in element E.
(d) State the valency of the element E.
Answer.

Question.10 Name the oxidising agent used for the conversion of ethanol to ethanoic acid. Distinguish between ethanol and ethanoic acid on the basis of (i) litmus test, (ii) reaction with sodium hydrogen carbonate.
Answer. Alkaline KMn04 or acidified potassium dichromate (K₂Cr₂O₇) are used for the conversion of ethanol to ethanoic acid.
Difference between ethanol and ethanoic acid

Question.14 State the meaning of inherited traits and acquired traits. Which of the two is not passed on to the next generation? Explain with the help of an example.
Answer. See Q. 17, 2012 (I Outside Delhi). [Page P – 47

Question.17 A 5 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 12 cm. The distance of the object from the lens is 8 cm. Using the lens forumla find the position, size and nature of the image formed.
Answer.

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