31/3/3 2019 Class 10 Science Question Paper Solution
SCIENCE
SECTION A
1) Define 1 kilowatt hour.
Ans: 1000 watt of power is used for 1 hour / commercial unit of energy / 3.6 x 106 J
2) Generally, we do not clean natural ponds or lakes but an aquarium needs periodic cleaning. Why ?
Ans: Lack of decomposers in aquarium.
SECTION B
3) List two causes of presbyopia. Draw labelled diagram of a lens used for the correction of this defect of vision.
Ans: Causes
i) gradual weakening of the ciliary muscles
ii) diminishing flexibility of the eye lens. (No diagram given in t.b. or reference books. Diagram for lens used, use a bifocal lens)
4) Show the formation of Na2O by the transfer of electrons.
Ans:
5) List in tabular form two differences between reflex action and walking.
Ans:
Reflex Action |
Walking |
– Reflex action is involuntary action
– It is controlled by spinal cord |
– Walking is voluntary action
– It is controlled by brain / cerebellum |
OR
List in tabular form two differences between pepsin and trypsin.
Ans:
Pepsin |
Trypsin |
-Secreted by the stomach
– It acts in acidic medium |
– Secreted by the Pancreas
– It acts in basic medium |
SECTION C
6) Name the process used to harness nuclear energy these days. Explain it briefly. List two advantages of using nuclear energy in place of fossil fuels.
Ans:
- Nuclear fission.
- When the nucleus of heavy atom is bombarded with low energy neutrons, can be split apart into lighter nuclei. When this is done, a tremendous amount of energy is released.
i) It releases 10 millions times / tremendous amount of energy produced by other fossil fuels.
ii) It can be used to generate clean electricity
iii) Self sustainable chain reaction
7) Why are forests considered ‘‘biodiversity hot spots’’ ? Suggest four approaches towards the conservation of forests.
Ans: Forests are rich reservoir of biodiversity containing a large number of plants and animals.
Approaches towards conservation of forests:
a) Help of local people should be taken / local people should be involved
b) Indiscriminate destruction of forest should be strictly prohibited.
c) Planting of trees should be increased.
d) Destruction of forests should not be done for making, roads, dams and hotels etc.
8) What is atmospheric refraction ? Explain with the help of a labelled diagram that the position of a star as seen by us is not its true position.
Ans:
- Bending of light due to the variation in optical density of the medium.
- The starlight, on entering into earth’s atmosphere undergoes continuous refraction before it reaches the earth.
- The since the atmosphere bends starlight towards the normal, the apparent position to the star is slightly different from its actual position
Diagram with correct labeling
OR
When do we consider a student sitting in the class to be myopic ? List two causes of this defect. Explain using a ray diagram how this defect of eye can be corrected.
Ans: (i) If the student cannot see the words written on the black board then he is considered myopic.
(ii) The defect may arise due to 1) Excessive curvature of the eyeball 2) Elongation of the eyeball.
(iii)
9) Write the chemical formula of washing soda. How can it be obtained from baking soda ? List two industries in which washing soda is used for other purposes than washing clothes.
Ans:
Na2CO3.10H20
In Glass, Soap and Paper Industry
10) Out of three metals P, Q and R, P is less reactive than Q and R is more reactive than P and Q both. Suggest an activity to arrange P, Q and R in order of their decreasing reactivity.
Ans:
Activity |
Observation |
Inference |
Put metal R in the sulphate solution of metal Q and P
Put metal P in the solution of sulphate ions of metal Q |
Solution becomes colourless in both the test tubes.
No reaction |
R displaces P and Q ions from their solutions.
P cannot displace Q ions from the solution |
OR
Name the ore of mercury. With the help of balanced chemical equations, explain the process of extraction of mercury from its ore.
Ans: Cinnabar / (HgS)
2HgS + 3O2 ->2HgO + 2SO2
11) (a) How is possible valency of an element determined from the electronic configuration of its atom ?
Ans: An element’s valency is determined by the number of electrons in its outer most shell.
(b) Determine the valency of an element X whose atomic number is 15.
Ans: Electronic configuration:
Atomic No. = 15
Electronic configuration of element X = 2,8, 5
Valency of Element X = 8 – 5 = 3
Hence the valency of element X is 3.
12) What is haemoglobin ? State the consequences of deficiency of haemoglobin in our bodies.
Ans: Respirator Pigment responsible for O2 transport.
Consequences:
Can affect the O2 supplying capacity of blood to the tissues
– Causes anaemia .
13) Explain the following :
(a) Speciation
Ans: Speciation: It refers to the process by which new species are formed from the pre-existing species
i) Geographical isolation
ii) Genetic drift
iii) Natural selection
(b) Natural Selection
Ans: ) Natural selection is the process by which organisms having some special features are at an advantage for better survival in the changed environment.
OR
Mendel, in one of his experiments with pea plants, crossed a variety of pea plant having round seeds with one having wrinkled seeds. State Mendel’s observations giving reasons of F1 and F2 progeny of this cross. Also, list any two contrasting characters, other than round seeds of pea plants that Mendel used in his experiments.
Ans:
- F1 generation – all plants with round seeds
- F2 generation – plants with round and wrinkled seeds.
- Tall / dwarf plants Yellow / green seeds White / purple flowers
14) Explain the ways in which glucose is broken down in absence or shortage of oxygen.
Ans: The first step in the breakdown of glucose. Glucose is converted to pyruvate.
Pyruvate in the absence of O2 may be converted to ethanol, CO2 and energy
Pyruvate in the shortage of O2 may be converted to lactic acid and energy.
15) List in tabular form three distinguishing features between cerebrum and cerebellum.
Ans:
Cerebrum |
Cerebellum |
1) It is a part of fore brain | 1) It is a part of hind brain |
2) It initiates intelligence, memory, voluntary movements etc. | 2) It maintains posture and equilibrium |
3) Main thinking part of the brain. | 3) Controls voluntary actions like walking in a straight line, picking up a pencil, riding a bicycle etc. |
SECTION D
16) (a) What is a hydrocarbon ? Give its one example.
Ans: Carbon compounds containing only carbon and hydrogen ore called hydrocarbons Example: Alkane / Alkene / Alkyne / any other
(b) Give the structural difference between saturated and unsaturated hydrocarbons with two examples each.
Ans:
(c) Name the following compounds :
Ans:
i)CH3 – OH
Methanol / Methyl alcohol
ii)
iii)
iv)
Ethanoic Acid / Acetic acid
17) (a) What is a double displacement reaction ? Explain with an example.
Ans: Exchange of ions in a reaction between two.
(b) A small amount of quick lime is added to water in a beaker.
Ans: Na2SO4 + BaCl2 -> BaSO4 + 2 NaCl
(i) Name and define the type of reaction that has taken place.
Ans: (i) Combination reaction: A combination reaction is a reaction where two or more elements or compounds combine to form a single compound.
(ii) Write balanced chemical equation for the above reaction and the chemical name of the product formed.
Ans: CaO + H2O Ca(OH)2
Quick lime Calcium Hydroxide
Chemical name of the product formed
(iii) List two main observations of this reaction.
Ans: Observations of the reactions:
– Reaction takes place vigorously
– Large amount of heat is released.
OR
(a) Design an activity to demonstrate the decomposition reaction of lead nitrate.
Ans: Activity : Take a pinch of lead nitrate powder in a test tube. Heat it over the flame
(b) Draw labelled diagram of the experimental set-up. List two main observations.
Ans:
Observation :
- Emission of brown fumes observed
- Reddish brown colour of residue
(c) Write balanced chemical equation for the reaction stating the physical state of the reactant and the products.
Ans:
18) (a) List four characteristics of the image formed by a concave lens of focal length 20 cm when the object is placed at a distance of 40 cm from its optical centre.
Ans:
- Virtual
- Erect
- Diminished
- On the same side of the object
(b) The size of image of an object by a convex lens of focal length 20 cm is observed to be reduced to 3 /1 rd of its size. Find the distance of the object from the optical centre of
Ans: Focal Length = 20cm.
u = – x cm
v=x/3
1/v-1/u=1/f
x=80cm
19) (a) Three resistors of resistances R1, R2 and R3 are connected (i) in series, and (ii) in parallel. Write expressions for the equivalentresistance of the combination in each case.
Ans:
- In series – RS=R1 + R2 + R3.
- In parallel – 1/Rp=1/R1+1/R2+1/R3
Resistance is at minimum – 1/Rp=1/R1+1/R2
1/12+1/12=2/12=6Ω
Resistance is maximum –Rs= R1+ R2
Rs=12+12=24 Ω
P=v2/R
Power ration in parallel and series = 4:1
(b) Two identical resistors of 12 W each are connected to a battery of 3 V. Calculate the ratio of the power consumed by the resulting combinations with minimum resistance and maximum resistance.
Ans: Pmin/Pmas=V2/Rmin/V2/Rmas=Rmas/Rmin=24=4/1
OR
(a) Write the relation between resistance and electrical resistivity of the material of a conductor in the shape of a cylinder of length ‘l’ and area of cross-section ‘A’. Hence derive the S.I. unit of electrical resistivity.
Ans:
Rαl
Rα1/A
Rα1/A
R=p1/A
p=RA/1=ohm ×m2
=ohm × m
(b) Resistance of a metal wire of length 5 m is 100 W. If the area of cross-section of the wire is 3 ´ 10–7 m2, calculate the resistivity of the metal.
Ans:
p=RA/1
=100 ×3×10-7/5
=60×10-7 ohm×m
20) (a) Name and state the rule to determine the direction of force experienced by a current carrying straight conductor placed in a uniform magnetic field which is perpendicular to it.
Ans:
- The rule is Fleming’s left hand rule.
- If the finger points in the direction of the magnetic field and the second finger in the direction of the magnetic field and the second finger in the direction of current then the thumb will point in the direction of motion or the force acting on the conductor
(b) Draw a labelled diagram of an electric motor.
Ans: Electric motor.
21) (a) What is reproduction ? List its two types.
Ans: Reproduction- The process of producing offsprings / young ones of its own kind.
Types:
i) Asexual
ii) Sexual
(b) How are the modes of reproduction different in unicellular and multicellular organisms ?
Ans:
Unicellular Organisms |
Multicellular Organisms |
Only one parent is required | Two parents are required |
It is a fast process of reproduction. | Slower process of reproduction than in unicellular organisms. |
No specialized cells are required for reproduction. | Specialized cells are required for reproduction. |
OR
(a) What are Sexually Transmitted Diseases (STD) ? List two viral and two bacterial STDs.
Ans: STD- A disease that can be transmitted through sexual contact.
- Viral – i)Warts ii) AIDS
- Bacterial- i) Gonorrhoea ii) Syphilis
(b) What is contraception ? List three reasons for adopting contraceptive methods.
Ans: Contraception: The method of preventing unwanted pregnencies, Reasons –
i) To prevent unwanted pregnancies
ii)To control population rise / birth rate
iii)To prevent transfer of STD’s iv)Proper gap between successive births v)For the better health of mother
SECTION E
22) In the experiment of preparing a temporary mount of a leaf peel to observe stomata, we use two liquids other than water. Name these two liquids and state when and why these liquids are used.
Ans: a) Saffranin is used to stain the material for better view.
b) Glycerine is used to avoid drying of peel.
OR
List four precautions in proper sequence which we observe while preparing a temporary mount of a leaf peel.
Ans: i) Take a thin peel of leaf on a glass slide.
ii) Stain it with saffranin
iii) Remove extra stain
iv) Put a drop of glycerin and cover it with cover slip
23) A student has set up an apparatus to show that ‘‘CO2 is released during respiration’’. After about 1 hour he observes no change in the water level in the delivery tube. Write two possible reasons for the failure of the experiment.
Ans: i) Conical flask is not air tight.
ii) Freshly prepared solution of KOH not used.
iii) Germinating seeds may be dry.
24) Consider the scale of a voltmeter shown in the diagram and answer the following questions :
(a) What is the least count of the voltmeter ?
Ans: 0.15V is the least count
(b) What is the reading shown by the voltmeter ?
Ans: The reading shown is 1.8V
(c) If this voltmeter is connected across a resistor of 20 W, how much current is flowing through the resistor?
Ans: R= 20Ω V=1.8V I=v/R =1.8/20=.09amp
25) List in proper sequence the steps of the experiment for determining the approximate focal length of a given concave mirror by obtaining the image of a distant object.
Ans: i) Fix a concave mirror on a stand and place it near a source of bright light
ii) Place a screen fitted on a stand in front of the mirror
iii) Move the screen back and forth, until a sharp and clear image of a distance object line a tree is obtained on the screen
iv) Mark the position of mirror and screen on the scale and note the distance between them
OR
A student has to trace the path of a ray of light passing through a rectangular glass slab for four different values of angle of incidence. (a) Write two important precautions for this experiment.
Ans: The student should take the following precaution
(a) Precaution –
(i)See that the pins are in a straight line and atleast 3cm apart.
(ii)Angle of incidence should be between 300 to 600 .
(iii) Glass slab should always remain inside the boundary.
(b) List two conclusions the student will draw based on his experiment.
Ans: Conclusion –
(i) The emergent ray is parallel to incident ray
(ii) Lateral displacement takes place.
(iii) Angle of incidence = Angle of emergence
26) List the conclusions you will draw while studying the following properties of ethanoic acid :
(a) Odour
Ans: Odour – it smells like vinegar
(b) Solubility in water
Ans: It is soluble in water
(c) Effect on litmus paper
Ans: Blue litmus to red
(d) Reaction with sodium hydrogen carbonate
Ans: NaHCO3 + CH3COOH -> CH3COONa + H2O + CO2
27) What is observed after about 1 hour of adding the strips of copper and aluminium separately to ferrous sulphate solution filled in two beakers ? Name the reaction if any change in colour is noticed. Also, write chemical equation for the reaction.
Ans:
- Putting Cu strips in FeSO4 — no reaction
- Putting Al strips in FeSO4 — change in colour observed
- Displacement reaction
- Al+FeSO4 -> Al2(SO4)3+Fe
Or
A student wants to study a decomposition reaction by taking ferrous sulphate crystals. Write two precautions he must observe while performing the experiment
Ans: 1) Do not point the mouth of boiling tube at your neighbours or yourself / point the test tube away from the body
2) Hold the test tube in inclined position
3) Hold the test tube with Tongs
CBSE Class 10 Previous Question Paper 2019 Solution
- Science (Set No 31/1/1)
- Science (Set No 31/1/2)
- Science (Set No 31/1/3)
- Science (Set No 31/2/1)
- Science (Set No 31/2/2)
- Science (Set No 31/2/3)
- Science (Set No 31/3/1)
- Science (Set No 31/3/2)
- Science (Set No 31/3/3)
- Science (Set No 31/4/1)
- Science (Set No 31/4/2)
- Science (Set No 31/4/3)
- Science (Set No 31/5/1)
- Science (Set No 31/5/2)
- Science (Set No 31/5/3)