31/2/3 2019 Class 10 Science Question Paper Solution
SCIENCE
SECTION A
1) Why does the cord of an electric oven not glow while its heating element does ?
Ans: Cord is made up of copper wire whereas heating element is made up of alloy.
2) Although coal and petroleum are produced by the degradation of biomass, yet we need to conserve these resources. Why ?
Ans: They are non renewable / their formation takes millions of years / exhausted in the future.
SECTION B
3) What is atmospheric refraction ? List two phenomena which can be explained on the basis of atmospheric refraction.
Ans: Refraction of light due to variation in optical density of earth.
Two phenomenon:- (i) Twinkling of stars (ii) Advance sunrise & delayed sunset
4) Name a metal of medium reactivity and write three main steps in the extraction of this metal from its sulphide ore.
Ans: (i) Iron / Zinc / Lead (any one)
(ii) Concentration of ore Enrichment/ of ore
(iii) Roasting / conversion of sulphide into oxide on heating in air
(iv) Reduction of metallic oxide to metal
5) List two chemical properties on the basis of which ethanol and ethanoic acid may be differentiated and explain how.
Ans: (i) Ethanoic acid reacts with NaOH to give sodium salt and water but C2H5OH does not show this reaction.
(ii) Ethanoic acid reacts with NaHCO3(Sodium Bicarbonate) or Na2CO3(Sodium Carbonate) and given sodium salt of ethanoic acid, water and carbon dioxide.
OR
Unsaturated hydrocarbons contain multiple bonds between two carbon atoms and these compounds show addition reactions. Out of saturated and unsaturated carbon compounds, which compounds are more reactive ? Write a test to distinguish ethane from ethene.
Ans: Unsaturated compounds are more reactive. Test: Bayer’s reagent test / Bromine water test given by ethene not by ethane / Ethane gives clear flame while ethene gives a yellow flame with lots of black smoke.
SECTION C
6) What happens to a beam of white light when it gets refracted through a glass prism ? Which colour deviates the most and the least after refraction through a prism ? What is likely to happen if a second identical prism is placed in an inverted position with respect to the first prism ?Justify your answer.
Ans: The white light splits into seven colours when it gets refracted through the glass prism (VIBGYOR)
The colour deviates most – Violet
The colour deviates least – Red
Colours disappear and again white light obtained.
OR
A student needs spectacles of power – 0·5 D for the correction of his vision.
(i) Name the defect in vision the student is suffering from.
Ans: Myopia
(ii) Find the nature and focal length of the corrective lens.
Ans: Concave / diverging lens and focal Length = 200cm
(iii) List two causes of this defect.
Ans: a) excessive curvature of the eye lens
(b) elongation of eye ball
7) Define a food chain. Design a terrestrial food chain of four trophic levels. If a pollutant enters at the producer level, the organisms of which trophic level will have the maximum concentration of the pollutant in their bodies ? What is this phenomenon called ?
Ans: Chain of organisms formed as a result of eating or being eaten by organisms is called food chain / A series of organisms feeding on one another, is called food chain.
Grass (Producer) -> Insect (grasshopper) (Herbivore) -> Frog (Carnivore) -> Snake (Top Carnivore)
– Tertiary trophic level / snake
– Biological magnification / Biomagnification
8) What are solar cells ? Explain the structure of solar panel. List two principal advantages associated with solar cells.
Ans: A device that converts solar energy directly into electrical energy.
A large no. of solar cells are combined in an arrangement called Solar Cell Panel.
Principal Advantages –
(i) They have no moving parts
(ii) require little maintenance & work quite satisfactorily without the use of any focusing device
(iii) These cells can be set up in remote & inaccessible areas where laying of a power transmission may be expensive.
9) During the reaction of some metals with dilute hydrochloric acid, the following observations were made by a student :
Explain these observations giving appropriate reason.
(a) Silver does not show any change.
Ans: Silver is placed below Hydrogen in reactivity series / among least reactive metal / Silver does not react with dil. Hydrochloric acid.
(b) Some bubbles of a gas are seen when lead is reacted with the acid.
Ans: Rate of reaction is slow / bubbles of Hydrogen gas are formed / lead lies above hydrogen in reactivity series.
(c) The reaction of sodium is found to be highly explosive.
Ans: Sodium is highly reactive / reaction is highly exothermic, evolving Hydrogen gas, which catches fire.
(d) The temperature of the reaction mixture rises when aluminium is added to the acid.
Ans: Reaction is exothermic
10) Given below are the steps for the extraction of copper from its ore. Write the chemical equation of the reactions involved in each case.
(i) Roasting of copper (I) sulphide
(ii) Reduction of copper (I) oxide from copper (I) sulphide
(iii) Electrolytic refining
Ans:
11) (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
12) What is a homologous series of carbon compounds ? Give an example and list its three characteristics.
Ans:
- A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series.
- Example – Alkane / Alkene / Alkyne / Alcohol or any other one correct example.
- Characteristics:-
i) They have same general formula
ii) They have same functional group
iii)The difference in the molecular mass of two successive member in 14μ
iv) The difference in the molecular formula of two successive member is of CH2
(v) They have similar chemical properties.
13) 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.
14) List in tabular form three distinguishing features between autotrophic nutrition and heterotrophic nutrition.
Ans:
Autotrophic Nutrition |
Heterotrophic Nutrition |
They can prepare their own food | They cannot prepare their own food. |
They require raw materials like CO2, H2O in the presence of sunlight and chlorophyll to prepare their food. | They depend on other plants & animals for their food. |
They store the food in the form of starch. | They store the food in the form of glycogen. |
15) (a) Budding, fragmentation and regeneration, all are considered as asexual mode of reproduction. Why ?
Ans: Because these methods involve only one parent / organisms are formed as a result of mitotic division / progeny (organisms) are similar in their genetic makeup and no variations.
(b) With the help of neat diagrams, explain the process of regeneration in Planaria.
(i) Planaria can be cut into any number of pieces and each piece grows through specialized cells into a complete organism.
SECTION D
16) A 6 cm tall object is placed perpendicular to the principal axis of a concave mirror of focal length 30 cm. The distance of the object from the mirror is 45 cm. Use mirror formula to determine the position, nature and size of the image formed. Also draw labelled ray diagram to show the image formation in this case.
Ans: Given –
h = 6 cm
f = –30 cm
v = –45 cm
mirror formula
1/f = 1/v + 1/u
1/v = 1/f – 1/u
=- 1 /30 – 1/ (−45)
=- 1/ 30 + 1 /45 = − 1 /90
f = – 90cm from the pole of mirror
Size of the image
m = −v/u
=-(90/45)=-2
h1=-2 x 6cm
=-12cm
Image formed will be real, inverted and enlarged.
Well labelled diagram
OR
An object 6 cm in size is placed at 50 cm in front of a convex lens of focal length 30 cm. At what distance from the lens should a screen be placed in order to obtain a sharp image of the object ? Find the nature and size of the image. Also draw labelled ray diagram to show the image formation in this case.
Ans: Given –
f = +30 cm
u = –50 cm
h = 6.0 cm
lens formula
1/f = 1/v − 1/u
1/v=1/f+1/u
=1/30-1/50
5-3/150=2/150=1/75
5-3/150=2/150=1/75
v=+75cm
m=v/u-h1/h
=75/-50-h1/h
h1=-9cm
Image formed is real, inverted and enlarged
Well labelled diagram
17) 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.
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) (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:
20) What is sexual reproduction ? Explain how this mode of reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution ?
Ans:
- When male and female organisms are involved in producing young ones, is known as sexual reproduction / Gametes from two organisms of opposite sex must fuse to produce young ones.
- Gametes (germs cells) produced are the products of meiosis / due to combining of DNA from two individuals, this results in mixing of characters and causes variations.
- In asexual reproduction, single parent produces young ones. There is no mixing of characters.
- More variations help in the process of evolution. Helpful variations accumulate over time and produce new species and result in evolution
21) (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..
SECTION –E
22) 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)
23) 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
24) 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
25) 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.
26) 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
27) 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
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)