31/2/2 2019 Class 10 Science Question Paper Solution
SCIENCE
SECTION A
1) Write two advantages associated with water harvesting at the community level.
Ans: (i) Recharged the ground water level
(ii) Brought rivers back to life
2) Should the resistance of a voltmeter be low or high ? Give reason.
Ans: High, In parallel connection, less current passes through high resistance.
SECTION B
3) Draw electron dot structure of carbon dioxide and write the nature of bonding between carbon and oxygen in its molecule.
Ans: Double covalent bond / covalent bond
OR
List two properties of carbon which lead to the huge number of carbon compounds we see around us, giving reason for each.
Ans: (i) Catenation / ability to form long chains of carbon atoms/ self linking property. Reason:- very strong carbon – carbon bond
(ii) Tetravalency / valency of four Reason:- All the four valencies of carbon atom are occupied with other elements.
4) Give reason :
(a) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Ans: It is easier to obtain a metal from its oxide as compared to sulphide and carbonate ore.
(b) Aluminium is a highly reactive metal; still it is widely used in making cooking utensils.
Ans: Aluminium forms a thicker protective oxide layer/anodizing.
5) The power of a lens is +5 diopters. What is the nature and focal length of this lens ? At what distance from this lens should an object be placed so as to get its inverted image of the same size ?
Ans: p=+5D
f=1/p=100/5=20cm
Nature of lens= convex(converging)
Distance is 40cm (at C)
SECTION C
6) List two types of the transport system in human beings and write the functions of any one of these.
Ans: (i) Blood circulatory system
(ii) Lymphatic system / lymph or tissue fluid
Functions of blood circulatory system
(i) Transport of oxygen
(ii) Transport of digested food
(iii) Transport of carbon dioxide
(iv) Transport of nitrogeneous waste
(v) Transport of salts
Functions of lymphatic system:-
(i) Carries digested and absorbed fat
(ii) Drains extra fluid from tissue
(extra cellular space) back into the blood
7) Distinguish between pollination and fertilisation. Mention the site and the product of fertilisation in a flower.
Ans: Pollination:- Transfer of pollen grains from stamen/anther to stigma.
Fertilization;- Fusion of male & female gamete
Site of fertilisation:- Ovary/ Ovule
Product ; Zygote
8) What is transpiration ? List its two functions.
Ans:
- The loss of water in the form of vapour from the aerial parts/leaves/stems is known as transpiration.
- Functions:-
(i) It helps in the absorption and upward movement of water
(ii) movement of dissolved minerals from root to leaves.
(iii) It helps in the temperature regulation or cooling of the plant.
OR
(a) What is translocation ? Why is it essential for plants ?
Ans: The transport of soluble products of photosynthesis (food or glucose) from one part to the other parts of the plant. To provide food to all parts of the plant.
(b) Where do the substances in plants reach as a result of translocation ?
Ans: Root, fruits, seeds and other growing organs/parts of the plant.
9) A student holding a mirror in his hand, directed the reflecting surface of the mirror towards the Sun. He then directed the reflected light on to a sheet of paper held close to the mirror.
(a) What should he do to burn the paper ?
Ans: Move the mirror/paper to focus the rays at one point
(b) Which type of mirror does he have ?
Ans: Concave mirror
(c) Will he be able to determine the approximate value of focal length of this mirror from this activity ? Give reason and draw ray diagram to justify your answer in this case.
Ans: Yes, distance between mirror and focal point gives approximate focal length.
OR
A 10 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 18 cm. Find the nature, position and size of the image formed.
Ans: 1 /v – 1/ u = 1/ f ∴ 1 /v = 1 /f + 1 /u
∴ 1/ v = 1 /12 + 1/ (−18)
∴ v = 36cm
m =v/u =h/h = ∴ m =
=> 36 /−18 = h / 10
=> h=-20cm (size of the image)
Nature of image – Real and inverted
10) List three environmental consequences of using fossil fuels. Suggest three steps to minimise the pollution caused by various energy sources.
Ans: Consequences :-
(i) Cause air pollution
(ii) The acidic oxides lead to acid rain
(iii) High concentration of green house gas (CO2)and its effect
(iv) Global Warming
Steps to minimize the pollution
(i) Use of alternate source of energy
(ii) Use of various devices to reduce emission of harmful gases.
(iii) By increasing efficiency of combustion process
11) Write the essential function performed by ozone at the higher levels of the Earth’s atmosphere ? How is it produced ? Name the synthetic chemicals mainly responsible for the drop of amount of ozone in the atmosphere. How can the use of these chemicals be reduced ?
Ans: It shields the surface of the earth from the UV radiation from the sun.
Chloro Fluoro Carbons (CFC’s)
Reduce the use of CFC’s by (a) minimizing the leakage through air conditioners and refrigerators / finding substitute chemicals that are ozone friendly.
12) (a) While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid ?
Ans: The process of diluting an acid is highly exothermic, and on the addition of acid to the water the excess heat is absorbed by water.
(b) Dry hydrogen chloride gas does not change the colour of dry litmus paper. Why ?
Ans: Because HCl does not form H+ /H3O + ions in dry condition.
OR
How is sodium hydroxide manufactured in industries ? Name the process. In this process a gas X is formed as by-product. This gas reacts with lime water to give a compound Y, which is used as a bleaching agent in the chemical industry. Identify X and Y and write the chemical equation of the reactions involved.
Ans:
- When electricity is passed through an aqueous solution of sodium chloride (brine)
- Chlor – alkali process
- X – Cl2
- Y = CaOCl2
- 2NaCl(aq) + 2H2O(l) -> 2NaOH(aq) + Cl2(g) + H2(g)
- Ca(OH)2 + Cl2 -> CaOCl2 + H2O
13) On heating blue coloured powder of copper (II) nitrate in a boiling tube,black copper oxide, O2 and a brown gas X is formed.
(a) Identify the type of reaction and the gas X.
Ans: Decomposition / Thermal decomposition,
The gas X is NO2 or (nitrogen dioxide)
(b) Write balanced chemical equation of the reaction.
Ans:
(c) Write the pH range of aqueous solution of the gas X.
Ans: Range less than 7 (or O——6.9pH)
14) Which compounds are called (i) alkanes, (ii) alkenes and (iii) alkynes ? C4H10 belongs to which of these ? Draw two structural isomers of this compound.
Ans:
Alkane |
Alkene |
Alkyne |
Saturated Hydrocarbon
With c-c Single Bond |
Unsaturated Hydrocarbon
with double bond in c=c |
Unsaturated Hydrocarbon
with triple bond in c≡c |
Alkane
2 structural isomers
15) What are amphoteric oxides ? Give an example. Write balanced chemical equations to justify your answer.
Ans:
- Metal oxides showing both acidic and basic nature
- Example: Al2O3 / ZnO (or any other)
Al2O3 + 6HCl -> 2AlCl3 + 3H2O
Al2O3 + 2NaOH -> 2NaAlO2 + H2O
SECTION D
16) (a) What are dominant and recessive traits ?
Ans: The trait which expresses itself in F1 (first) generation after crossing contrasting (opposite) traits is known as dominant character (trait).
Recessive Trait: The trait which is not expressed itself in F1(first) generation after crossing contrasting (opposite) trait.
(b) ‘‘Is it possible that a trait is inherited but may not be expressed in the next generation ?’’ Give a suitable example to justify this statement.
Ans: Yes
17) (a) Why is the use of iodised salt advisable ? Name the disease caused due to deficiency of iodine in our diet and state its one symptom.
Ans:
- Iodine is essential for functioning of thyroid / formation of thyroxine hormone
- Disease is Goitre
- Swollen neck
(b) How do nerve impulses travel in the body ? Explain.
Ans: Impulse travels from dendrite to cell body, then along the axon to its end. At the end some chemicals are released which fill the gap of synapse, and starts a similar electrical impulse to another neuron and the impulse further travel in the body.
OR
What is hydrotropism ? Design an experiment to demonstrate this phenomenon.
Ans: The movement/response of part of plant (root) towards water Experiment:-
(i) Soak the seeds in water overnight
(ii) Place moist cotton in a perforated petridish
(iii) Put the soaked seeds in the petridish & place it on a beaker
(iv) Roots pass through pores and grow downwards.
(v) After sometime roots will bend towards base of petridish having moisture..
18) (a) How will you infer with the help of an experiment that the same current flows through every part of a circuit containing three resistors in series connected to a battery ?
Ans: (i) Join the three resistors of different values in series
(ii) Connect them with battery, an ammeter and plug key.
(iii) Plug the key and note the ammeter reading
(iv) Change the position of ammeter to anywhere in between the resistors and note the ammeter reading each time.
(v) The ammeter reading will remain same everytime. Therefore when resistors are connected in series same current flows through all resistors, when it is connected to a battery.
(b) Consider the given circuit and find the current flowing in the circuit and potential difference across the 15 W resistor when the circuit is closed.
Total resistance of the circuit =
R = R1 + R2 + R3 = 5 + 10 + 15 = 30 ohm
Potential difference across the circuit / By ohm’s law
V = IR or I = v/R=30V/30ohm=1A
Potential difference across 15 ohm Resistor = 1A X 15 ohm = 15 volt
OR
(a) Three resistors R1 , R2 and R3 are connected in parallel and the combination is connected to a battery, ammeter, voltmeter and key. Draw suitable circuit diagram and obtain an expression for the equivalent resistance of the combination of the resistors.
Ans: Total current I = I1 + I2 + I3 Let RP be the equivalent resistance of R1, R2, R3. Then the total current I = v/Rp
(i) On applying ohm’s law for each R1, R2,R3
I1 = v/R1 , I2 = v/R2, I3 = v/R3
∴ I = V (1/R1+1/R2+1/R3)=V/Rp
∴ 1/Rp+ 1/R1+ 1/R2+1/R3
(b) Calculate the equivalent resistance of the following network :
Ans:
1/Rp=1/20+1/20=2/20=1/10
=> Rp=10 ohms
Equivalent resistance of the network = Req = R1 + Rp = 10 + 10 = 20 ohm
19) Draw the pattern of magnetic field lines produced around a current carrying straight conductor passing perpendicularly through a horizontal cardboard. State and apply right-hand thumb rule to mark the direction of the field lines. How will the strength of the magnetic field change when the point where magnetic field is to be determined is moved away from the straight conductor ? Give reason to justify your answer.
Ans:
Statement of right hand thumb rule.
The magnetic field strength decreases with increase of distance from the current carrying conductor.
Reason: There is inverse relation between field strength and distance from current carrying conductor.
20) (a) What is scattering of light ? Explain how the colour of the scattered light depends on the size of the scattering particles.
Ans: Scattering: Direction of ray of light changes when it collides with particles of comparable size.
– Fine particle scatter shorter wavelengths like blue light.
– Particles of larger size scatter longer wavelengths like red light.
– If particle size is large enough scattered light may appear white.
(b) Explain the reddish appearance of the Sun at sunrise or sunset. Why does it not appear red at noon ?
Ans:
- During sunrise and sunset, sun is near horizon. Sunlight travels longer distance. Most of blue light scatters away by particles. Light of longer wavelength reaches our eye so sun appears reddish.
- At noon, sun is directly overhead so sunlight travels lesser distance. Less amount of blue light is scattered giving white appearance to sun
Or can be explained with the help of a diagram given below
21) (a) List any three observations which posed a challenge to Mendeleev’s Periodic Law.
Ans: (i) No fixed position of H in the periodic table.
(ii) Position of isotopes not clear.
(iii) Atomic mass does not increase in a regular manner.
(b) How does the metallic character of elements vary on moving from
(i) left to right in a period,
Ans: Left to right metallic character decreases
Reason: Effective nuclear charge increases / tendency to loose electrons decrease / electro positivity decreases
(ii) from top to bottom in a group of the Modern Periodic Table ?
Give reason for your answer.
Ans: Top to bottom metallic character increases
Reason :- Size of atom increase/tendency to loose electron increases
OR
The electrons in the atoms of four elements A, B, C and D are distributed in three shells having 1, 3, 5 and 7 electrons respectively in their outermost shells. Write the group numbers in which these elements are placed in the Modern Periodic Table. Write the electronic configuration of the atoms of B and D and the molecular formula of the compound formed when B and D combine
Ans:
SECTION E
22) List four precautions which a student should observe while preparing a temporary mount of a leaf peel to show stomata in his school laboratory.
Ans: (i) Size of the leaf peel should be very small.
(ii) Put peel immediately in the drop of water.
(iii) Place cover slip carefully to avoid the air bubbles.
(iv) It should not be overstained.
(v) No fold in the peel
23) List in proper sequence four steps of obtaining germinating dicot seeds.
Ans: (i) Soaking of seeds
(ii) Emergence of radicle
(iii) Splitting of cotyledons
(iv) Emergence of plumule
OR
After examining a prepared slide under the high power of a compound microscope, a student concludes that the given slide shows the various stages of binary fission in a unicellular organism. Write two observations on the basis of which such a conclusion may be drawn.
Ans:
(i) Elongation of nucleus
(ii) Constriction appears due to the division of the cytoplasm
24) The current flowing through a resistor connected in a circuit and the potential difference developed across its ends are as shown in the diagram by milliammeter and voltmeter readings respectively :
(a) What are the least counts of these meters ?
Ans: ∠ least count of ammeter = 10 mA
∠ least count of Voltmeter = 0.1 V
(b) What is the resistance of the resistor ?
Ans: 2.4/0.25=9.6 ohm(250mA=0.25A)
25) Draw the path of a ray of light when it enters one of the faces of a glass slab at an angle of nearly 45°. Label on it (i) angle of refraction, (ii) angle of emergence and (iii) lateral displacement.
Ans:
Labelling
- Angle of refraction (r1)
- Angle of emergence (e)
- Lateral displacement (ML)
OR
A student traces the path of a ray of light through a glass prism as shown in the diagram, but leaves it incomplete and unlabelled. Redraw and complete the diagram. Also label on it Ði, Ðe, Ðr and ÐD.
Ans:
Labelling of ∠i + ∠e + ∠r & ∠D
26) What is observed when a pinch of sodium hydrogen carbonate is added to 2 mL of acetic acid taken in a test tube ? Write chemical equation for the reaction involved in this case.
Ans:
- Brisk effervescense of CO2
- CH3COOH + NaHCO3 -> CH3COONa + CO2+H2O
27) A teacher provided acetic acid, water, lemon juice, aqueous solution of sodium hydrogen carbonate and sodium hydroxide to students in the school laboratory to determine the pH values of these substances using pH papers. One of the students reported the pH values of the given substances as 3, 12, 4, 8 and 14 respectively. Which one of these values is not correct ? Write its correct value stating the reason.
Ans:
- The pH value of water given is incorrect.
- Its correct value is 7 it is neutral in nature.
OR
What would a student report nearly after 30 minutes of placing duly cleaned strips of aluminium, copper, iron and zinc in freshly prepared iron sulphate solution taken in four beakers ?
Ans:
- There will be no reaction in the beakers having Fe strip & Cu strip.
- The solution having Al & Zn strip will show reaction / the solution of FeSO4 having Al & Zn strip will become colourless.
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)