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CBSE CLASS X - SCIENCE MOST IMPORTANT QUESTION FOR 2019

Q.no Questions Year of

Repetition Q.1 Write chemical equation of the reaction of ethanoic acid with

the following: (a) Sodium; (b) Sodium hydroxide; (c) Ethanol. Write the name of one main product of each reaction.

2016, 2017

Q.2 a) List two reasons for the appearance of variations among the progeny formed by sexual reproduction. b) (i) Name the part marked ‘A’ in the diagram. (ii) How does ‘A’ reach part ‘B’? (iii) State the importance of the part ‘C’. (iv) What happens to the part marked ‘D’ after fertilization is over?

2014, 2016

Q.3 How do Mendel’s experiment show that traits are inherited independently?

2016, 2017

Q.4 List four stakeholders which may be helpful in the conservation of forests.

2016, 2015

Q.5 Why is sustainable management of natural resources necessary? out of the two methods-reuse and recycle -which one would you suggest practicing and why?

2012, 2014, 2015

Q.6 What is homologous series of carbon compounds? Write the molecular formula of two consecutive members of homologous series of aldehydes . State which part of these compounds determines their: I) physical and II) chemical properties.

2012, 2014

Q.7 What is vegetative propagation? Write two of its advantages. 2011, 2012 Q.8 Explain AIDS. List any four methods of prevention (control) of

AIDS. 2011, 2012

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Q.9 Na, Mg, Al are the elements having one, two, three valence electrons respectively. Which of these elements (I) has the largest atomic radius, (II)is least reactive? Justify your answer stating reason for each.

2012, 2015

Q.10 List and explain in brief three methods of contraception. 2012, 2015 Q.11 List in tabular form two distinguishing features between

acquired traits and inherited traits, with one example of each. 2012, 2013, 2015, 2017

Q.12 A 4cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 24cm. The distance of the object from the lens is 16cm. Find the position, size and nature of the image formed, using the lens formula.

2012, 2015

Q.13 What is the function of ozone at the higher level of atmosphere?

2012, 2015

Q.14 The time difference between the actual sunset and the apparent sunset is about 2 minutes. What is the reason for the same? Explain with the help of a diagram.

2011, 2012

Q.15 Why are forest considered “biodiversity hot spots”? List two ways in which an individual can effectively contribute to the management of forests and wildlife.

2012, 2015, 2016,

Q.16 I) We see eyes in planaria, insects, octopus and vertebrates. Can eyes be grouped together in case of the above- mentioned animals to establish a common evolutionary origin? Why? II)State one evidence to prove that birds have evolved from reptiles.

2012, 2015

Q.17 Write the number of vertical columns in the modern periodic table. What are these columns called?

2012, 2013, 2017

Q.18 What is meant by biodiversity? List two advantages of conserving forest and wildlife.

2015, 2012

Q.19 Write the name and formula of the 2nd member of homologous series having general formula CnH2n+2.

2014, 2015

Q.20 Write the help of labelled diagram, explain why the sun appears reddish at the sun-rise and sun-set.

2015, 2016

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Q.21 a) State the laws of refraction of light. Explain the term absolute refractive index of a medium and write an expression to relate it with the speed of light in vacuum. b) The absolute refractive indices of two media ‘A’ and ‘B’ are 2.0 and 1.5 respectively. If the speed of light in medium ‘B’ is 2x108m/s, calculate the speed of light in: I) Vacuum, II) Medium ‘A’.

2015, 2018

Q.22 What is speciation? 2013, 2015 Q.23 Why should biodegradable and non -biodegradable wastes

be discarded in two separate dustbins? 2013, 2015

Q.24 From the following elements: 4Be,9F,19K,20Ca I) The element having one electron in the outermost shell. II) Two elements of the same group

2012, 2015

Q.25 What is sustainable management? Why is reuse considered better in comparison to recycle?

2012, 2014, 2017

Q.26 List any four reason for vegetative propagation being practiced in the growth of some type of plants.

2011, 2012

Q.27 What does HIV stand for? Is AIDS an infectious disease? List any four modes of spreading AIDS.

2011, 2012

Q.28 Write the molecular formula of first two members of homologous series having functional group -Cl.

2012, 2017

Q.29 An object of height 2.5 cm is placed at a distance of 15 cm from the optical centre ‘O’ of a convex lens of focal length 10 cm. Draw a ray diagram to find the position and size of the image formed. Mark optical centre ‘O’, principal focus F and height of the image on the diagram.

OR An object of height 4.0 cm is placed at a distance of 30 cm from the optical centre ‘O’ of a convex lens of focal length 20 cm. Draw a ray diagram to find the position and size of the image formed. Mark optical centre ‘O’ and principal focus ‘F’ on the diagram. Also find the approximate ratio of size of the image to the size of the object.

2016, 2018

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Q.30 a) Draw a ray diagram to show the formation of image of an object placed between infinity and the optical centre of a Concave lens. b) A concave lens of focal length 15 cm forms an image 10 cm from the lens. Calculate i) the distance of the object from the lens ii) the magnification for the image formed iii) the nature of the image formed

OR (a) Draw a ray diagram to explain the term angle of deviation. (b) Why do the component colours of incident white light split into a spectrum while passing through a glass prism, explain? (c) Draw a labeled ray diagram to show the formation of a Rainbow.

OR Draw a ray diagram to show the path of the refracted ray in each of the following cases: i) passing through its optical centre. ii) parallel to its principal axis. iii) directed towards its principal focus. OR A person cannot read newspaper placed nearer than 50cm from his eyes. Name the defect of vision he is suffering from. Draw a ray diagram to illustrate this defect. List its two possible causes. Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length

2011, 2017, 2014, 2013

Q.31 State any four characteristics of the image of an object formed by a plane mirror.

OR 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.

2011, 2017

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Q.32 If the image formed by a spherical mirror for all positions of the object placed in front of it is always erect and diminished, what type of mirror is it? Draw a labelled ray diagram to support your answer.

OR State the type of mirrors used for i) headlights and ii) rear view mirrors, in cars and motorcycles. Give reason to justify your answer in each case.

OR Mention the types of mirrors used as i) rear view mirrors, ii) shaving mirrors. List two reasons to justify your answers in each case.

2012, 2013, 2018

Q.33 In the following ray diagram the correctly marked angle are

(a) ∠ i and ∠ e (b) ∠ A and ∠ D (c) ∠ i, ∠ e and ∠ D (d) ∠ r, ∠ A and ∠ D

OR After tracing the path of a ray of light through a glass prism a student marked the angle of incidence(∠i), angle of refraction(∠r) angle of emergence(∠e) and the angle of deviation (∠D) as shown in the diagram. The correctly marked angles are :

2016, 2015, 2017

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1. ∠i and ∠r 2. ∠i and ∠e 3. ∠i,∠e and ∠D 4. ∠i,∠r and ∠e

OR 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

Q.34 After tracing the path of rays of light through a glass slab for three different angles of incidence, a student measured the corresponding values angles of refraction r and angle of emergence e and recorded them in the table given below :

2013, 2014

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The correct observation are : A. I and II B. II and III C. I and III D. I,II and III

OR After tracing the path of a ray of light passing through a rectangular glass slab for four different values of the angle of incidence, a student reported his observations in tabular form as given below :

The best observation is A. I B. II C. III D. IV

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Q.35 Study the following diagrams in which the path of a ray of light passing through a glass prism as traced by four students P,Q,R and S is shown

The student who has traced the path correctly is (A P (B) Q (C) R (D) S

OR While performing the experiment to trace the path of a ray of light passing through a glass prism, four students marked the incident ray and the emergent ray in their diagrams in the manner shown below.

2013, 2014

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The correct path of the rays has been shown by : (A) I (B) II (C) III (D) IV

Q.36 A student traces the path of a ray of light passing through a rectangular glass slab and marks the angle of incidence i, angle of refraction r and angle of emergence e, as shown.

The correctly marked angles(s) is/are (A)∠i only (B)∠e only (C)∠r only (D)∠i and ∠e

OR The correct sequence 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 :

2014, 2017

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a. 2,4,1,3 b. 2,1,4,3 c.1,2,4,3 d.2,1,3,4

Q.37 A student focussed the Sun rays using an optical device ‘X’ on a screen S as shown.

From this it may be concluded that the device ‘X’ is a (select the correct option) A. Convex lens of focal length 10 cm. B. Convex lens of radius of curvature 20 cm. C. Convex lens of focal length 20 cm. D. Concave mirror of focal length 20 cm.

OR A student focussed the image of a distant object using a device ‘X’ on a white screen ‘S’ as shown in the figure. If the distance of the screen from the device is 40 cm , select the correct statement about the device.

A. The device X is a convex lens of focal length 20 cm. B. The device X is a concave mirror of focal length 40 cm.

2013, 2014, 2015

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C. The device X is a concave mirror of radius of curvature 40 cm. D. The device X is a convex lens of focal length 40 cm.

OR Study the following diagram and select the correct statement about the device ’X’:

A) Device ‘X’ is a concave mirror of radius of curvature 12cm. B) Device ‘X’ is a concave mirror of focal length 6 cm. C) Device ‘X’ is a concave mirror of focal length 12cm. D) Device ‘X’ is a concave mirror of focal length 12 cm.

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Answers

Ans 1. a.) 2CH3COOH + 2Na → 2CH3COONa (Sodium ethanoate/sodium acetate)+ H2

b.) CH3COOH+NaOH →CH3COONa(Sodium ethanoate/sodium acetate)+H2O

c.) CH3COOH +C2H2OH → CH3COOC2H5(Ethyl ethanoate/ester) + H20

Ans 2.

a) I) Involvement of two different individuals

II) Creation of new combination of variants

b) I) pollen/pollen grain

II) by pollination/ agents of pollination

III) It ( pollen tube) helps male gamete to reach egg (ovule)

IV) Converts into embryo

Ans 3. When a cross was made between a tall pea plant with round seeds and a short pea plant with wrinkled seeds, the F1 progeny plants are all tall with round seeds: this indicates that tallness and round seeds are the dominant traits.

When the F1 plants are self pollinated the F2 progeny consisted of some tall plants with round seeds and some short plants with wrinkled seeds which are the parental traits 1.

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There were also some new combinations like tall plants with wrinkled seeds and short plants with round seeds 1⁄2.

Thus, it may be concluded that tall and short traits and round and wrinkled seed traits have been inherited independently

Ans 4.

1. Local people living in villages near the forest.

2. Industrialists who use forest produce as raw materials.

3. Wildlife and nature enthusiasts.

4. Forest department of the government.

Ans 5.

▪ 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.

▪ A type of management which encourages utilization of resources that meet current basic human needs while preserving the resources for the needs of future generations.

▪ Reuse is better as it does not consume energy.

▪ sustainable management encourages all forms of growth that are needed to meet basic human needs, while conserving natural resources for the future generations. It necessary because, our natural resources are exhaustible, limited and non-renewable.

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▪ Our resources are being over exploited by the growing population and there is no equitable distribution of resources as a handful of rich and powerful people are exploiting the to built for short term benefits. So it is necessary.

Ans 6. Homologous series Homologous series are a series of carbon compound with regularly varying chain lengths and the same functional group. Adjacent compound differs by CH2 unit and H4 molecule mass.

CH3- CHO, CH3CH2-CHO are two consecutive member, of homologous series of aldehydes.

I. The carbon Chain length determines physical properties.

II. The functional group determines chemical properties.

Ans 7. Vegetative propagation is practised for growing some types of plant because plants grown by this method bear flower and fruits earlier than the plants grown from seeds. plant grown by this method are genetically similar to the parent plant and have some characteristics this method makes because the propagation of plant which have lost the ability to produce seeds. survival rats of plants grown by this method is more than that of seed grown plants.

Ans 8. AIDS stands for Acquired Immune Deficiency Syndrome. Four methods of preventing (control) of aids are following:

1. Avoid contact with infected blood.

2. Be careful with syringe and surgical equipment.

3. Use condoms.

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4. Get tested and treated for STDs.

Ans 9.

I) Na / Sodium.

Reason – The atomic size decreases from left to right due to the increase in the nuclear charge.

II) Al / Aluminium.

Reason – The tendency to lose electrons decreases from left to right.

Ans 10. Four methods –

I) Mechanical or barrier method OR Male or female condoms

II) Use of hormonal preparations OR Oral Pills / I-pill / Saheli

III) Use of loop or copper T OR IUCD

(iv) Surgical method OR tubectomy / vasectomy

Ans 11. Acquired Traits

▪ Does not bring about change in the DNA of the germ cell.

▪ Cannot be passed on to the progeny.

▪ Cannot direct evolution.

Examples: Acquiring knowledge, loss of weight or any other example

Inherited Traits

▪ Brings about change in the DNA of the germ cell.

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▪ Can be passed on to the progeny.

▪ Can direct evolution.

(any two) Examples: Skin colour, colour of the eye or any other example.

Ans 12. Height of object ho = 4 cm

Focal length of convex lens = 24 cm

Object distance u = -16 cm

Image distance v = ?

Image height hi = ?

Lens formula: 1/v - 1/u = 1/f

1/v = 1/f + 1/u

= 1/24 + 1/(-16)

= -1/48

⇒ v = - 48 cm

The image distance is 48 cm on the same side of the lens as the object.

Magnification m = v/u = (-48)/(-16) = 3 = hi/ho = hi/3

⇒ hi = 3 x 3 = 9 cm

The image is enlarged and erect.

So a virtual, erect, enlarged image is formed at 48 cm from the optic center on the same side of the lens as the object is positioned.

Ans 13. The ozone molecules in the upper atmosphere (stratosphere) and the

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lower atmosphere (troposphere) are chemically identical, because they all consist of three oxygen atoms and have the chemical formula O3. However, they have very different roles in the atmosphere and very different effects on humans and other living beings. Stratospheric ozone (sometimes referred to as "good ozone") plays a beneficial role by absorbing most of the biologically damaging ultraviolet sunlight (called UV-B), allowing only a small amount to reach the Earth's surface. The absorption of ultraviolet radiation by ozone creates a source of heat, which actually forms the stratosphere itself (a region in which the temperature rises as one goes to higher altitudes). Ozone thus plays a key role in the temperature structure of the Earth's atmosphere.

Ans 14. It happens because sun rays bends slightly towards the earth surface when it is below the horizon due to the presence of various layers of atmosphere which refracts the the sunlight in various amounts towards the earth surface...This is because of the refraction of the light from the Sun by the Earth's atmosphere--the Earth's atmosphere bends the path of the light so that we see the Sun in a position slightly different from where it really is. The magnitude of this effect varies with latitude, but it's strongest at the equator, where the Sun rises 2 minutes earlier than it would if the Earth had no atmosphere, and sets 2 minutes after it would if the Earth had no atmosphere.

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Ans 15. Because large number of life forms / range of life forms (such as bacteria, fungi, fern, nematodes, insects, birds, reptiles, mammals, gymnosperms and angiosperms) are found there / A region with large biodiversity of endangered species, many of them being highly endemic and such regions being subjected to large scale destruction are designated as “Hot spots” by ecologists.

• Two ways –

I) Not allowing cutting of trees

II) To promote / make people aware about the importance of forests and wildlife.

III) Not using wild life products / fur coat or any other named product.

Ans 16.

I) No, the structure of the eye in each of the organisms is different.

II) Fossils of certain dinosaurs / reptiles show imprints of feathers along with their bones but they could not fly presumably using the feathers for insulation; Later they developed / evolved and adapted feathers for flight, thus becoming the ancestors of present day birds. (OR any other suitable evidence/example)

Ans 17. In chemistry, a group (also known as a family) is a column of elements in the periodic table of the chemical elements. There are 18 numbered groups in the periodic table, but the f-block columns (between groups 2 and 3) are not numbered.

Ans 18. A region with large biodiversity of endangered species, many of them being highly endemic and such regions being subjected to large scale destruction are designated as “Hot spots” by ecologists.

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Four measures:

▪ Reforestation of the deforested areas as soon as possible.

▪ Ban on the indiscriminate cutting of trees.

▪ Felling of trees for fuel wood should be avoided.

▪ Overgrazing in forests should be discouraged.

Ans 19. Name : Ethane

Formula : C2H6

Ans 20.

▪ Light from the Sun near the horizon passes through thicker layers of air and longer distance.

▪ Most of the blue light and shorter wavelengths of sunlight are scattered away by the particles. Light of larger wavelength reaches us giving the reddish appearance

Ans 21. a) Statement of laws of Refraction of light (two laws)

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When a ray of light travels from vacuum or air into a given medium then ratio of sin i to sin r is called absolute refractive index of the medium.

Ans 22. Speciation: The process of formation of one or more new species from an existing species is called speciation. Speciation occurs when the gene pool of a population is somehow reproductively isolated from other sister population of the parent species and gene flow no longer occurs between them. Then a population splits into independent species. Which become reproductively isolated from each other.

On basis of period taken in speciation there are two types of mechanism of speciation.

Ans 23. So that the time and energy required in segregation may be saved and waste may be disposed off quickly

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Ans 24.

I) K / Potassium.

II) Be and Ca.

• KX or KCl

• Ionic / Electrovalent

Ans 25. Sustainable Management -

It is a pattern of management that promises the use of natural resources in such a way that they meet the human needs not only in the present but also in the future.

Advantage of Reuse over Recycling Reusing a material is better that recycling it because recycling requires a large amount of energy and money. Reuse, on the other hand, preserves the embodied energy originally used in manufacturing an item. Reuse also creates less air and water pollution than recycling.

Ans 26. Four reasons why vegetative propagation is practised in the growth of some type of plants are;

I. As some plants do not produce seeds.

II. It is a cheaper, easier and a rapid method.

III. To maintain the character and traits of certain plants. The plants produced by this method are genetically similar.

IV. Used in methods such as layering or grafting to grow many plants like sugarcane, roses, or grapes for agricultural purposes.

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Ans 27. HIV stands for human immunodeficiency virus. AIDS stand for acquired immunodeficiency syndrome. Usually it's don't spread by air, water, touch, etc.

But AIDS spread by -

▪ Sex (vaginal, anal or oral) with person suffering from HIV+.

▪ Mother to baby (by the birth or after feeding milk).

▪ By blood.

Ans 28. Molecular formula of first two members of homologous series having functional group -Cl.

▪ CH3Cl

▪ C2H5Cl

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Important Questions for other Subjects

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Resources

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