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CBSE-XII-2017 EXAMINATI
CBSE – X – 2016 EXAMINATION
SCIENCE
SET-3
Time: 3 Hrs
...
Marks: 90
General Instructions:
1
...
You are to attempt both the sections
...
All questions are compulsory
...
There is no choice in any of the questions
...
All questions of Section A and all questions of Section B are to be attempted separately
...
Question numbers 1 to 3 in Section A are one-mark questions
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6
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These are to be answered in about 30 words each
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Question numbers 7 to 18 in Section A are three-mark questions
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8
...
These are to be answered in about 70 words each
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Question numbers 25 to 33 in Section B are multiple choice questions based on practical skills
...
You are to select one most appropriate response out of the four provided to you
...
Question numbers 34 to 36 in Section B are two-marks questions based on practical skills
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SECTION A
Question 1
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Solution: 1-butanal
Marks: 1
Question 2
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Solution: Two functions of the ovaries of the human female reproductive system are
1
...
To secrete the female hormones oestrogen and progesterone
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In a food chain of frog, grass, insect and snake, assign trophic level to frog
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Marks: 1
Question 4
...
If
speed of light in glass is 2 × 108 m/s, find the speed of light in water
...
vedantu
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Marks: 2
Question 5
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Solution: Four stakeholders which may help in the conservation of forests are
1
...
People who live in and around the forest and are dependent on forest produce to lead their lives
3
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Forest and wildlife activists who want to see forests in their original form
...
The construction of large dams leads to social and environmental problems
...
Solution: Social problems arise because the construction of dams causes the displacement of a large number
of tribals and peasants who are then rendered homeless
...
Construction of dams leads to several environmental problems such as deforestation and loss of biodiversity
because large areas of forest land get submerged in water leading to an ecological imbalance
...
The position of eight elements in the Modern Periodic Table is given below where atomic
numbers of elements are given in the parenthesis
...
2
Li(3)
Be(4)
3
Na(11)
Mg(12)
4
K(19)
Ca(20)
5
Rb(37)
Sr(38)
(i) Write the electronic configuration of Ca
...
(iii) What is the number of shells in Sr?
(iv) Predict whether K is a metal or a non-metal
...
Solution: (i) Electronic configuration of Ca (20): 2, 8, 8, 2
(ii) Rb belongs to Group 1, and all Group 1 elements have one valence electron
...
(iv) K is a metal with electronic configuration 2, 8, 8, 1
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(v) The atomic size increases down the group and decreases across a period
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(vi) Be < Mg < Ca < Rb
Marks: 3
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Question 8
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Write balanced chemical equation in each case
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Solution: Three different chemical reactions showing the conversion of ethanoic acid to sodium ethanoate:
2CH3COOH + Na2CO3
2CH3COONa + H2O + CO2
CH3COOH + NaHCO3
CH3COONa + H2O + CO2
CH3COOH + NaOH
CH3COONa + H2O + CO2
Marks: 3
Question 9
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(a) Determine the valence electrons and the valency of `X’
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(c) Write the name and formula of the compound formed when `X’ combines with chlorine
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(c) Atomic number of Cl = 17
Electronic configuration = 2, 8, 7
Valency of Y = 1
Molecular formula of the compound formed when ‘X’ reacts with an element ‘Y’ is XCl3
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An element `X’ has mass number 35 and number of neutrons 18
...
Also write group number, period number and valency of `X’
...
Marks: 3
Question 11
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(b)
(i) Name the part marked `A’ in the diagram
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(iv) What happens to the part marked `D’ after fertilisation is over?
Solution: (a) Two reasons for the appearance of variations among the progeny formed by sexual
reproduction are
1
...
2
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(b)
(i) Part ‘A’ labelled is pollen grain
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The pollen grain reaches the stigma during pollination
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The pollen tube carries the gametes to the embryo sac for fertilisation
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After fertilisation with the male gametes, the egg cell forms the zygote
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Define reproduction
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Reproduction maintains the number of chromosomes specific to a species in each generation
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So, when these germ cells from 2 different
individuals combine during sexual reproduction to form a new individual, it results in the re-establishment
of the number of chromosomes and the DNA content in the new generation
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Marks: 3
Question 13
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Describe
briefly how regeneration is carried out in multicellular organisms like Hydra
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When a hydra is bisected anywhere in the upper 7th or 8th part of the body column, the upper half will
regenerate a foot at its basal end and the lower half will regenerate a head at its apical end; each half
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generates the organ which it is missing
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Marks: 3
Question 14
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Justify this
statement
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After a certain body design comes into existence, it will shape the effects of all other subsequent
design changes simply because it already exists
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This means that the
classification of life forms will be closely related to their evolution
...
However, other groups of organisms have acquired their particular body designs relatively recently
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Marks: 3
Question 15
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For example, he crossed a pea plant having yellow colour and round seed characters with
another pea plant bearing green colour and wrinkled seed characters
...
This indicated that traits separated from their original
parental combinations and got inherited independently
...
vedantu
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The activities of man had adverse effects on all forms of living organisms in the biosphere
...
The unfavourable conditions created by man himself threatened the
survival not only of himself but also of the entire living organisms on the mother earth
...
(a) Why is it necessary to conserve our environment?
(b) State the importance of green and blue dust-bins in the safe disposal of the household waste
...
Solution: (a) It is necessary to conserve our environment because
(i) It helps in protecting the ozone layer
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(iii) It provides us with many useful products such as medicines and wood
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It will be very useful in
the separate disposal of biodegradable and non-biodegradable wastes
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(c) Two values exhibited are
(i) Creating environmental awareness among students and society
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Marks: 3
Question 17
...
If the
image is at a distance of 30 cm from the mirror, where is the object placed? Find the focal length of the
mirror
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Solution: Given: Magnification, m = –2
Distance of the image, v = –30 cm
v
Magnification, m =
u
v
(30)
u
m
(2)
u = –15 cm
Substituting these values in the mirror formula
1 1 1
f v u
1
1
(30) (15)
1
1
f
10
f = –10 cm
When the object is moved 10 cm towards the mirror the new position of the object is
u' = – (15 – 10) = –5 cm
Substituting the new value in the mirror formula
1 1 1
f v u'
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1 1 1 1
1
v' f u' 10 (5)
1 1
v' 10
v' = 10 cm
Thus, the image is located 10 cm behind the mirror
...
Thus, the image is erect, virtual and magnified in nature
...
Describe an activity to show that colours of white light splitted by a glass prism can be
recombined to get white light by another identical glass prism
...
Solution: The seven colours of a spectrum can be recombined to give back white light as
1
...
When a beam of light is allowed to fall on the surface of one prism, a patch of ordinary white light
is obtained on a screen placed behind the second prism
...
The first prism disperses the white light into seven coloured rays
...
This is because the
refraction produced by the second prism is equal and opposite to that produced by the first prism
...
Marks: 3
Question 19
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(i) What should be the range of distance of an object placed in front of the mirror?
(ii) Will the image be smaller or larger than the object? Draw ray diagram to show the formation of image in
this case
...
Show the positions of pole, principal focus and the centre of curvature in the above ray diagrams
...
e
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Here, the focal length of the mirror is 12 cm
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(ii) The image will be larger than the object (enlarged)
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e
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Marks: 5
Question 20
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How does it occur? Describe how fossils provide us evidences in support of
evolution
...
Accumulation of variation in genetic material forms the basis of evolutionary processes
...
Fossils tell us how species have changed across long periods of the Earth’s history
...
Some invertebrates living on the sea bed died and were buried in the sand
...
More sand was accumulated and formed sandstone under pressure
...
After millions of years, dinosaurs living in the area died and their bodies were buried in the mud
...
The mud got compressed into the rock, just above the rock containing earlier invertebrate fossils
...
Again millions of years later, the bodies of horse-like creatures dying in the area were fossilised in the
rocks above the earlier rocks
...
Much later, because of erosion and water flow, some rocks wore out and exposed the horse-like fossils
...
What is placenta? Describe its structure
...
Solution: The placenta is an organ attached to the lining of the womb during pregnancy
...
It contains blood spaces on the
mother’s side and villi on the embryo’s side
...
It provides food and oxygen to the foetus
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vedantu
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The foetus gives away waste products and carbon dioxide to the mother’s blood for excretion
...
A carbon compound `P’ on heating with excess conc
...
One molecule of `R’ on combustion forms two molecules of carbon dioxide and three molecules of
water
...
Excess H2SO4
H2 /Nickel catalyst
O2
Solution: P
Q
R
2CO2 + 3H2O
Excess H2SO4
P
Q
Excess H2SO4
CH3CH2OH
CH2 = CH2
H2 /Nickel catalyst
Q
R
H2 /Nickel catalyst
CH2 = CH2
CH3 – CH3
O2
R
2CO2 + 3H2O
O2
CH3 – CH3
2CO2 + 3H2O
Excess H2SO4
H2 /Nickel catalyst
O2
CH3CH2OH
CH2 = CH2
CH3 – CH3
2CO2 + 3H2O
P
Q
R
Ethanol
Ethene
Ethane
Marks: 5
Question 23
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Draw diagrams to illustrate your answers
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The light seems to be bright and dim as it keeps changing because of
continuous refraction through the different layers of the atmosphere of the Earth
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(b) The sunrise is advanced because of the atmospheric refraction of sunlight
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A ray of sunlight entering the Earth's atmosphere
follows a curved path because of atmospheric refraction before reaching the Earth
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For an observer on the Earth, the apparent
position of the Sun is slightly higher than the actual position
...
The increased atmospheric refraction of sunlight occurs also at sunset
...
The advanced sunrise and delayed sunset increase the duration of the day by four minutes
...
(a) Define focal length of a divergent lens
...
Use lens formula to determine the distance of the object
from the lens and the size of the image formed
...
vedantu
...
Solution: (a) The focal length of a diverging lens is half the value of its radius of curvature
...
(b) Given:
f = −20 cm (It is a diverging lens
...
)
Using the lens formula,
1 1 1
f v u
1 1 1
u v f
1
1
1
( 15) ( 30)
30
u 30 cm
Given: Height of the object, h = 6 cm
Height of the image, h' = ?
v h'
Magnification, m =
u h
v
(15)
h' h 6
u
(30)
h' 3 cm
(c)
Marks: 5
SECTION B
Question 25
...
On examining the list the teacher remarked that only three parts are correct
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vedantu
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Testa, tegmen and micropyle are the
parts of the seed coat
...
If you are asked to select a group of two vegetables, out of the following, having homologous
structures which one would you select?
(a) Carrot and radish
(b) Potato and sweet potato
(c) Potato and tomato
(d) Lady finger and potato
Solution: (a) Carrot and radish
Homologous structures are fundamentally same in structure and origin but are modified to perform different
functions in different organisms
...
From the given plants, carrot and radish
are homologous structures because they both are underground roots
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Marks: 1
Question 27
...
The angle between the normal and the emergent ray is the angle of emergence
...
vedantu
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In your laboratory you trace the path of light rays through a glass slab for different values of
angle of incidence ( i ) and in each case measure the values of the corresponding angle of refraction ( r )
and angle of emergence ( e )
...
According to Snell’s law, we get
sin i
sin r
For glass > 1
sin r < sin i
or r < i
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In refraction of light through a glass slab, the emergent ray is parallel to the incident ray
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Marks: 1
Question 29
...
The image obtained on the serene, as
compared to the object is always:
(a) Laterally inverted and diminished
(b) Inverted and diminished
(c) Erect and diminished
(d) Erect and highly diminished
Solution: (b) inverted and diminished
Images obtained on the screen are always diminished and inverted in nature
...
Suppose you have focused on a screen the image of candle flame placed at the farthest end of
the laboratory table using a convex lens
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Marks: 1
Question 31
...
Which of the following
combinations of an oil and a base would be best suited for the preparation of soap?
(a) Castor oil and calcium hydroxide
(b) Turpentine oil and sodium hydroxide
(c) Castor oil and sodium hydroxide
(d) Mustard oil and calcium hydroxide
Solution: (a) P and Q
Dissolving chloride salts of calcium or magnesium in distilled water will make the water hard and lather
formation will take place with difficulty
...
A student puts a drop of reaction mixture of a saponification reaction first a blue litmus paper
and then on a red litmus paper
...
(b) There is no change in the red litmus paper and the blue litmus paper turns red
...
(d) No change in colour is observed in both the litmus papers
...
vedantu
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So, when a student puts
a drop of reaction mixture of a saponification reaction first on a blue litmus paper and then on a red litmus
paper, he will observe that there is no change in the blue litmus paper and the red litmus paper turns blue
...
In the neighbourhood of your school, hard water required for an experiment is not available
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Marks: 1
Question 34
...
Name this process and draw diagrams, of what he observes, in a proper
sequence
...
Different stages of budding as observed by
the student are depicted below:
Marks: 2
Question 35
...
5 cm is placed at a distance of 15 cm from the optical centre `O’ of a
convex lens of focal length 10 cm
...
Mark optical `O’, principal focus F and height of the image on the diagram
...
vedantu
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A student adds a spoon full of powdered sodium hydrogen carbonate to a flask containing
ethanoic acid
...
Also write chemical equation foe the reaction
...
(ii) It is a neutralisation reaction and heat is released
...
vedantu