CBSE Class 10 Science Previous Question Paper 2017 Solution
SECTION-A
1) Write the molecular formula of first two members of homologous series having functional group –Cl.
Ans: CH3 Cl, C2H5Cl
2) Name the method by which spirogyra reproduces under favourable conditions. Is this method sexual or asexual ?
Ans: Fragmentation Asexual.
3) What is an ecosystem ?
Ans: A unit of biosphere in which biotic and abiotic components interact with each other.
4) An object is placed at a distance of 30 cm in front of a convex mirror of focal length 15 cm. Write four characteristics of the image formed by the mirror.
Ans: Virtual, erect, diminished, laterally inverted
5) What is sustainable management ? Why is reuse considered better in comparison to recycle ?
Ans: Management of resources in a way that present day needs of the population are justified as well as they remain available for future generation.
Reuse does not consume energy.
6) Management of forest and wild life resources is a very challenging task. Why ? Give any two reasons.
Ans: Space (Clearing forests) is needed for developmental activities.
Our selfish attitude/ No respect for natural resources.
(or same explained in any other manner)
7) Two carbon compounds X and Y have the molecular formula C H4 8 and C H5 12 respectively. Which one of these is most likely to show addition reaction ? Justify your answer. Also give the chemical equation to explain the process of addition reaction in this case.
Ans: C4H8, it is an unsaturated hydrocarbon due to the presence of a double bond.
8)Complete the following chemical equations :
Ans:
9) Write the names given to the vertical columns and horizontal rows in the Modern Periodic Table. How does the metallic character of elements vary on moving down a vertical column ? How does the size of atomic radius vary on moving left to right in a horizontal row ? Give reason in support of your answer in the above two cases.
Ans: Vertical Columns – Groups
Horizontal Rows – Period
Metallic character increases
Reason: Ability to lose electrons increases on moving down the group due to increase in distance between the nucleus and the valence electrons /decrease in the attraction between the nucleus and the valence electrons.
Atomic radius decreases
Reason: the nuclear charge increases on moving from left to right across a period resulting in increase in the attraction between the nucleus and the valence electrons.
10) An element P (atomic number 20) reacts with an element Q (atomic number 17) to form a compound. Answer the following questions giving reason :
Write the position of P and Q in the Modern Periodic Table and the molecular formula of the compound formed when P reacts with Q.
Ans: Position of P Group – 2 Because it has 2 valence electrons/ 2, 8, 8, 2
Period – 4 Because it has 4 shells/ 2, 8, 8, 2
Position of Q Group – 17 Because it has 7 valence electrons/ 2, 8, 7
Period – 3 Because it has 3 shells/ 2, 8, 7
Formula PQ2 Because valency of P is 2 and that of Q is 1
11) What happens when :
(a) Accidently, Planaria gets cut into many pieces ?
Ans: Each piece regenerates into new Planaria
(b) Bryophyllum leaf falls on the wet soil ?
Ans: Bud, at its notches develop into new plants.
(c) On maturation sporangia of Rhizopus bursts ?
Ans: It releases spores which germinate into new mycelium in moist conditions.
12) State the basic requirement for sexual reproduction ? Write the importance of such reproductions in nature.
Ans: Formation of male and female gametes, fusion of gametes/ syngamy
Importance – Combination of DNA from two different individuals lead to increase in genetic variation in the organism
This leads to diversity in the population which helps in natural selection.
13) State the changes that take place in the uterus when :
(a) Implantation of embryo has occurred.
Ans: When implantation of embryo has occurred the uterine wall thickens and is richly supplied with blood to nourish the growing embryo.
(b) Female gamete / egg is not fertilised.
Ans: The thick and spongy lining of the uterus slowly breaks and comes out through the vagina as blood and mucus.
14) Distinguish between the acquired traits and the inherited traits in tabular form, giving one example for each.
Ans:
Acquired Trait |
Inherited Traits |
1) Develop during one’s life time |
Are inherited from the parents |
2) Do not bring about changes in the DNA of the germ cells |
Result due to existing changes in the DNA of the germ cells |
3) Cannot be passed on to the progeny |
Can be passed on to the progeny |
Examples |
|
Acquired knowledge, loss of weight | Skin colour, colour of the eye (any one) |
15) Explain with the help of an example each, how the following provide evidences in favour of evolution :
(a) Homologous organs
Ans: a) Homologous Organs – The study of these organs suggests that these organisms with organs having same structure but performing different functions have evolved from a common ancestor, e.g. forelimbs of different vertebrates.
(b) Analogous organs
Ans: Analogous Organs – The study of these apparently similar organs suggests that the organisms with apparently similar organs do not share common ancestory. Similarity in these organs is superficial/ Design and the structure of these organs are very different, e.g. Wings of bird and wings of butterfly.
(c) Fossils
Ans: Fossils – Provide the missing link between the species, e.g. Fossils of dinosaurs with feathers/ fossils of prehistoric horse/ or any other correct example.
16) An object 4 cm in height, is placed at 15 cm in front of a concave mirror of focal length 10 cm. At what distance from the mirror should a screen be placed to obtain a sharp image of the object. Calculate the height of the image.
Ans: h1 = + 4cm f = – 10cm u = – 15cm
1/f=1/v+1/u
→1/v=1/f-1/u
1/v=1/-10cm-1/-15cm
∴v=-30cm
h2/h1=v/u
∴ h2=-v/uxh1
=-(-30cm/-15cmx4cm
=-8cm
17) Due to gradual weakening of ciliary muscles and diminishing flexibility of the eye lens a certain defect of vision arises. Write the name of this defect. Name the type of lens required by such persons to improve the vision. Explain the structure and function of such a lens.
Ans: Presbyopia
Bifocal lens
Upper portion/ par
Presbyopia
Bifocal lens
Upper portion/ part Concave / Diverging lens
To view far off objects
Lower part Convex/ converging lens
To facilitate/ view nearby objects
18) You have been selected to talk on “ozone layer and its protection” in the school assembly on ‘Environment Day.’
(a) Why should ozone layer be protected to save the environment ?
Ans: Because Ozone layer protects/ shields earth from harmful UV radiations of the sun
(b) List any two ways that you would stress in your talk to bring in awareness amongst your fellow friends that would also help in protection of ozone layer as well as the environment.
Ans:
- Conducting poster making competition highlighting effects of ozone layer depletion.
- Conducting street plays highlighting the ways of environment protection.
19) Soaps and detergents are both types of salts. State the difference between the two. Write the mechanism of the cleansing action of soaps. Why do soaps not form lather (foam) with hard water ? Mention any two problems that arise due to the use of detergents instead of soaps.
Ans:
- Soaps are the sodium or potassium salts of long chain carboxylic acids while detergents are the ammonium or sulphonate salts of long chain carboxylic acids.
- The dirt is oily in nature and when soap is added to water, its molecules form structures called micelles in which carbon chain of the molecules dissolves in the oil while the ionic end dissolves in water and faces outside. The micelles thus help in dissolving the dirt in water. (Note: 1 mark to be awarded if only labelled diagram of micelle is given)
- Ca2+ and Mg2+ present in hard water form insoluble substance (scum) with soap.
- Two problems –
(i) Non-biodegradable
(ii) Water pollution / soil pollution
20) (a) Name the organ that produces sperms as well as secretes a hormone in human males. Name the hormone it secretes and write its functions.
- Ans: Testes
- Testosterone
- Functions of Testosterone –
I) Formation of sperms
II) Development of secondary sexual characters
(b) Name the parts of the human female reproductive system where fertilisation occurs.
Ans: Fallopian Tubes/ Oviduct
(c) Explain how the developing embryo gets nourishment inside the mother’s body.
Ans: Placenta, a special disc–like tissue embedded in the mother’s uterine wall and connected to the foetus/ embryo
Placenta provides a large surface area for glucose and oxygen/ nutrient to pass from the mother’s blood to the developing embryo/ foetus.
21) How do Mendel’s experiments show that
(a) traits may be dominant or recessive ?
Ans: a) Mendel conducted a Monohybrid cross/ (crossed pure tall pea plants with pure dwarf pea plants), observed only tall pea plants in the F1 generation, but on selfing the F1 progeny both tall and dwarf pea plants were observed in F2 generation in the ratio 3:1. Appearance of tall character in F1 and F2 generations shows tallness to be a dominant character. But absence of dwarf character in F1 and its reappearance in F2 confirms that dwarfness is a recessive character.
(b) inheritance of two traits is independent of each other ?
b) Mendel conducted a dihybrid cross and observed that though he started with two types of parents, he obtained four types of individuals in F2. The appearance of new recombination in F2 generations along with parental type characters show that traits are inherited independently of each other.
22) Analyse the following observation table showing 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 :
S. No. |
Object distance u (cm) |
Image distance v (cm) |
1 |
– 90 | + 18 |
2 | – 60 |
+ 20 |
3 |
– 30 | + 30 |
4 | – 20 |
+ 60 |
5 |
– 18 | + 90 |
6 | – 10 |
+ 100 |
(a) What is the focal length of the convex lens ? Give reason in support of your answer.
Ans: a) f = +15cm
Reason: Objects at S. No. (3) indicates u = -30cm, v = +30cm
\ f = 15 cm
(b) Write the serial number of that observation which is not correct. How did you arrive at this conclusion ?
Ans: Observation at S. No. (6)
The value, u = -10 cm , indicates that the object is in between the optical centre and the focus (i.e., less than the focal length) of the lens and hence the image should be on the same side as the object. Thus the image distance cannot be positive.
(c) Take an appropriate scale to draw ray diagram for the observation at S. No. 4 and find the approximate value of magnification.
Ans: c) u = -20cm ; v = + 60cm ; f = + 15 cm
m=h2/h1=-4.5cm/+1.5cm=-3
23) (a) To construct a ray diagram we use two rays which are so chosen that it is easy to know their directions after reflection from the mirror. List two such rays and state the path of these rays after reflection in case of concave mirrors. Use these two rays and draw ray diagram to locate the image of an object placed between pole and focus of a concave mirror.
Ans:
- Listing of any two (out of four) rays and stating their path after reflection from a concave mirror.
- Ray diagram
Using these two rays for the ray diagram when the object is in between the pole and the focus of the mirror.
(b) A concave mirror produces three times magnified image on a screen. If the object is placed 20 cm in front of the mirror, how far is the screen from the object ?
Ans: u = – 20cm m = – 3
m=v/-u
v = -m ´u
= – (- 3) (- 20 cm) = – 60 cm
Distance between the object and the screen is 40 cm
= – 60 cm – (- 20 cm) = – 40 cm
24) (a) Draw a ray diagram to explain the term angle of deviation.
Ans:
(b) Why do the component colours of incident white light split into a spectrum while passing through a glass prism, explain.
Ans: Different colour of white light bend through different angles with respect to the incident light, as they pass through the glass prism. Thus, each colour emerges along a different path, forming a spectrum.
(c) Draw a labelled ray diagram to show the formation of a rainbow.
Ans:
SECTION-B
25) You have four test tubes, A, B, C and D containing sodium carbonate, sodium chloride, lime water and blue litmus solutions respectively. Out of these the material of which test tube / test tubes would be suitable for the correct test of acetic / ethanoic acid ?
(a) only A
(b) A and B
(c) B and C
(d) A and D
Ans: (d) A and D
26) For demonstrating the preparation of soap in the laboratory which of the following combinations of an oil and a base would be most suitable ?
(a) Mustard oil and calcium hydroxide
(b) Castor oil and calcium hydroxide
(c) Turpentine oil and sodium hydroxide
(d) Mustard oil and sodium hydroxide
Ans: (d) Mustard oil and sodium hydroxide
27) A student took four test tubes P, Q, R and S and filled about 8 mL of distilled water in each. After that he dissolved an equal amount of Na SO 2 4 in P, K SO 2 4 in Q, CaSO4 in R and MgSO4 in S. On adding an equal amount of soap solution and shaking each test tube well, a good amount of lather will be obtained in the test tubes :
(a) P and Q
(b) P and R
(c) P, Q and S
(d) Q, R and S
Ans: (a) P and Q
28) A student while observing an embryo of a gram seed listed various parts of the embryo as listed below : Testa, Micropyle, Cotyledon, Tegmen, Plumule, Radicle. On examining the list the teacher commented that only three parts are correct. Select these three correct parts :
(a) Cotyledon, Testa, Plumule
(b) Cotyledon, Plumule, Radicle
(c) Cotyledon, Tegmen, Radicle
(d) Cotyledon, Micropyle, Plumule
Ans: (b) Cotyledon, Plumule, Radicle
29) Select the set of homologous organs from the following :
(a) Wings of pigeon and a butterfly
(b) Wings of bat and a pigeon
(c) Forelimbs of cow, a duck and a lizard
(d) Wings of butterfly and a bat
Ans: (c) Forelimbs of cow, a duck and a lizard
30) Three students A, B and C focussed a distant building on a screen with the help of a concave mirror. To determine focal length of the concave mirror they measured the distances as given below :
Student A : From mirror to the screen
Student B : From building to the screen
Student C : From building to the mirror
Who measured the focal length correctly :
(a) Only A
(b) Only B
(c) A and B
(d) B and C
Ans: (a) Only A
31) If you focus the image of a distant object, whose shape is given
below, on a screen using a convex lens,
Ans: c
32) In the following diagram the correctly marked angles are :
(a) ∠ A and ∠ e
(b) ∠ i, ∠ A and ∠ D
(c) ∠ A, ∠ r and ∠ e
(d) ∠ A, ∠ r and ∠ D
Ans: a
33) The correct sequencing of angle of incidence, angle of emergence,
angle of refraction and lateral displacement shown in the following
diagram by digits 1, 2, 3 and 4 is :
(a) 2, 4, 1, 3
(b) 2, 1, 4, 3
(c) 1, 2, 4, 3
(d) 2, 1, 3, 4
Ans: b
34) A gas is liberated immediately with a brisk effervescence, when you add acetic acid to sodium hydrogen carbonate powder in a test tube. Name the gas and describe the test that confirms the identity of the gas.
Ans: Carbon-dioxide/ CO2
Lime water turns milky on passing CO2 through it.
35) Name the type of asexual reproduction in which two individuals are formed from a single parent and the parental identity is lost. Write the first step from where such a type of reproduction begins. Draw first two stages of this reproduction.
Ans: Binary Fission
Elongation of cell and its nucleus
Correct diagram showing progressive elongation of the nucleus and cytoplasm.
36) A student places a candle flame at a distance of about 60 cm from a convex lens of focal length 10 cm and focuses the image of the flame on a screen. After that he gradually moves the flame towards the lens and each time focuses the image on the screen.
(a) In which direction-toward or away from the lens, does he move the screen to focus the image ?
Ans: Away from the lens
(b) How does the size of the image change ?
Ans: Size increases
(c) How does the intensity of the image change as the flame moves towards the lens ?
Ans: Intensity decreases
(d) Approximately for what distance between the flame and the lens, the image formed on the screen is inverted and of the same size ?
Ans: About 20 cm