31/1/3 2019 Class 10 Science Question Paper Solution
SCIENCE
SECTION-A
1) If you could use any source of energy for heating your food which one would you prefer? State one reason for your choice.
Ans:
- Fuel energy / microwave / hot plate / solar energy
- Easily available
2) Write the function of voltmeter in an electric circuit.
Ans: To measure potential difference across two points.
SECTION-B
3) What happens to the image distance in the normal human eye when we decrease the distance of an object, say 10 m to 1 m? Justify your answer.
Ans:
- Image distance remains the same.
- It is the distance between the eye lens and retina, which remains the same.
4) List two different function performed by pancreas in our body.
Ans:
- Image distance remains the same.
- It is the distance between the eye lens and retina, which remains the same.
5) How it can be proved that the basic structure of the modern periodic table is based on the electronic configuration of atoms of different elements?
Ans: Modern periodic table consists of groups and periods. Where number of valence electrons determines the group and number of shells determines the period.
OR
The electronic configuration of an element is 2, 8, 4. State its:
(a) group and period in the modern periodic table.
Ans: Group – 14, Period – 3
(b) name and write its one physical property.
Ans: Silicon
Non – metallic / poor conductor of electricity
SECTION-C
6) How can we help in reducing the problem of waste disposal?
Ans: Segregation of waste; Recycling; Composting: Reducing the use of non – biodegradable material: Reuse
OR
Define an ecosystem. Draw a block di8agram to show the flow of energy in an ecosystem.
Ans: The system where all the living organisms in an area together interact with the non – living constituents of the environment.
7) List three advantages each of:
(i) exploiting resources with short term aims,
Ans: Three advantages of exploiting resources with short term aims:
(i) Immediate benefit to few people.
(ii) Progress in science and technology for development in a country.
(iii) Urbanisation and Industrialisation of an area.
and
(ii) using a long term perspective in managing our natural resources.
Ans: Three advantages of using a long time perspective:
(i) Resources will be made available for sustainable development.
(ii) Provides valuable contribution to the socio-economic development.
(iii) Quality of environment will be conserved.
8) What is a rainbow? Draw a labelled diagram to show the formation of a rainbow.
Ans: Rainbow – A natural spectrum of sunlight appearing in the sky after a rain shower
9) Nervous and hormonal system together perform the function of control and coordination in human beings. Justify this statement with the help of an example.
Ans: For nervous and hormonal systems to control and coordinate in human beings, hypothalamus plays an important role in receiving the neural / nerve signals from brain and release hormones.
Ex – In situation of iodine deficiency, hypothalamus releases hormones to stimulate pituitary gland, it further sends stimulating hormone to thyroid gland to secrete thyroxine that regulates carbohydrate metabolism.
10) Trace the sequence of events which occur when a bright light is focused on your eyes.
Ans: Receptor Cells of eyes/retina–> Sensory Neuron–> Brain / CNS–> Pupil contracts / Eye lids close/blink <– Eye Muscles <– Eye Muscles
11) What is photosynthesis? Explain its mechanism.
Ans: A process in which green plants takes carbon dioxide and water and convert them into carbohydrates / food in the presence of sunlight and chlorophyll. Mechanism:
(i) Absorption of light energy by chlorophyll.
(ii) Conversion of light energy to chemical energy.
(iii) Splitting of water molecules into hydrogen and oxygen.
(iv) Reduction of carbon dioxide to carbohydrate.
12) Name the plant mendel used for his experiment. What type of progeny was obtained by Mendel in f1 and f2 generations when he crossed the tall and short plants? nWrite the ratio he obtained in F2 generation plants.
Ans:
- Pea Plant / Garden pea / Pisum sativum
- F1 – All tall; F2- Tall and short
- Ratio – Tall : Short
OR
List two differences between acquired traits and inherited traits by giving an example of each.
Ans:
Acquired Traits |
Acquired Traits |
These traits are not transferred from one generation to the next generation | These traits are transferred from one generation to the next |
They do not bring about change in DNA Example: Acquiring any skill | They bring about changes in DNA Example: Eye colour |
13) 2g of silver chloride is taken in a china dish and the china dish is placed in sunlight for sometime. What will be your observation in this case? Write the chemical reaction involved the form of a balanced chemical equation. Identify the type of chemical reaction.
Ans:
- White silver chloride turns grey in sunlight
- Decomposition reaction / Photolytic decomposition
OR
Identify the type of reactions taking place in each of the following cases and write the balanced chemical equation for the reactions.
(a) Zinc reacts with silver nitrate and silver.
Ans: Displacement reaction
Zn + 2 AgNO3à Zn (NO3)2 + 2 Ag
(b) Potassium iodide reacts with lead nitrate to produce potassium nitrate and lead iodide.
Ans: Double displacement reaction
2 KI + Pb (NO3)2à PbI2 + 2KNO3
14) Based on the group valency of elements write the molecular formula of the following compounds giving justification for each:
(i) Oxide of first group elements.
Ans: A2O – Valency of group one is 1 and of oxygen is 2
(ii) Halide of the elements of group thirteen, and
Ans: AX3 – Valency of group 13 is 3 and of halogen is 1
(iii) Compound formed when an element, A of group 2 combines with an element, B of group seventeen.
Ans: AB2– Valency of element A of group 2 is 2 and of element B of group seventeen is 1.
15) Explain the following:
(a) Sodium chloride is an ionic compound which does not conduct electricity in solid state where as it does conduct electricity in molten state as well as in aqueous solution.
Ans: In molten state, due to heat the electrostatic forces of attraction between the oppositely charged ions are overcome. So ions move freely and conduct electricity. In aqueous solutions ions are free and conduct electricity.
(b) Reactivity of aluminium decrease if it is dipped in nitric acid.
Ans: Due to the formation of a coating of aluminium oxide / Al2O3.
(c) Metals like calcium and magnesium are never found in their free state in nature.
Ans: Reactive metals like calcium and magnesium react easily with different elements and occur in the form of ores.
SECTION-D
16) With the help of a suitable circuit diagram prove that the reciprocal of the equivalent resistance of a group of resistances joined in parallel is equal to the sum of the resiprocals of the individual resistances.
Ans:
From figure:
I=I1+I2+I3
I1=V/R1, I2=V/R2, I3=V/R3
∴ V/Rp=V/R1+V/R2+V/R3
1/RP=1/R1+1/R2+1/R3
(b) In an electric circuit two resistors of 12 Ω each are joined in parallel to a 6 V battery. Find the current drawn from the battery.
Ans: R1=R2=12 Ω
V=6V
1/RP=1/R1+1/R2=1/12+1/12
∴ RP=6Ω
I=V/RP=6V/6V=1A
OR
An electric lamp of resistance 20 Ω and a conductor of resistance 4 Ω are connected to a 6 v battery as shown in the circuit. Calculate:
(a) the total resistance of the circuit,
Ans: R=R1+R2
=20Ω+4Ω=24Ω
(b) the current through the circuit,
Ans: 1=v/R
=6v/24Ω=0.25A
(c) the potential difference across the
(i) electric lamp
Ans: For electric lamp:
V=IR
=6/24×20 = 5 V
and
(ii) conductor,
Ans: For Conductor
V=IR
=6/24x 4=1v
and
(d) power of the lamp
P=VI
=5V x 6/24A=1.25W
17) (a)Draw magnetic field lines produced around a current carrying straight conductor passing through a cardboard. Name, state and apply the rule to make the direction of these field lines.
Ans:
- Rule – Right hand thumb rule Imagine that you are holding a current-carrying straight conductor in your right hand such that the thumb points towards the direction of current. Then your fingers will wrap around the conductor in the direction of the field lines of the magnetic field.
(b) 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 wire carrying constant current ? Justify your answer.
Ans:
- Strength decreases
- Reason – the concentric circles representing the magnetic field around a current-carrying straight wire become larger and longer as the distance increases.
18) An object is placed at a distance of 60 cm from a concave lens of focal length 30 cm.
(i) Use lens formula to find the distance of the image from the lens.
Ans: i) u = -60 cm f = -30 cm v = ?
1/f=1/v-1/u
∴ 1/v=1/f+1/u
=1/(-30cm)+1/(-60cm)=-3/60
∴V=-20cm
m=v/u=-20cm/-60cm=1/3
(ii) List four characteristic of the image (nature, position, size, erect/inverted) formed by the lens in this case.
Ans: Nature:- Virtual
Position:- 20 cm from lens on the same side as the object
Size:- Diminished Erect/Inverted:- Erect
(iii) Draw ray diagram to justify your answer of part(ii).
Ans:
19) Define pollination. Explain the different types of pollination. List two agents of pollination? How does suitable pollination lead to fertilization?
Ans:
- Pollination – Transfer of pollen from anther / stamen to stigma of the flower
- Type of Pollination – a) Self pollination – Transfer of pollen from anther / stamen to stigma occurs in the same flower b) Cross pollination – Pollen is transferred from anther / stamen of one flower to stigma of another flower
- Agents of pollination – Wind, Water, Insects and Animals
- A tube grows out of the pollen grain and travels through the style, to reach the female germ cell in the ovary to cause fertilization
OR
(a) Identify the given diagram. Name the part 1 to 5.
Ans:
- Female reproductive system
- Name of parts –
1) Fallopian tube/Oviduct
2) Ovary
3) Uterus
4) Cervix
5) Vagina
(b) What is contraception? List three advantages of adopting contraceptive measures.
Ans:
- Method to avoid pregnancy
- Advantages
– Proper gap between two pregnancies
– Avoiding unwanted pregnancy
– Keeping population under control
20) Write the chemical formula and name of the compound which is the active ingredient of all alcoholic drinks. List its two uses. Write chemical equation and name of the product formed when this compound reacts with-
Ans:
- C2H5OH, Ethanol/Ethyl alcohol
- Good solvent; used in medicines
(i) Sodium metal
Ans: Good solvent; used in medicines
2C2H5OH + 2 Naà 2C2H5ONa + H2
Sodium ethoxide
(ii) hot concentrated sulphuric acid
Ans:
Ethene
OR
What is methane? Draw its electron dot structure. Name the type of bonds formed in this compound. Why are such compounds:
Ans:
- CH4/Simplest hydrocarbon
- Covalent bonds
(i) poor conductors of electricity?
Ans: No ions or charged particles are formed
and
(ii) have low melting and boiling points? What happens when this compound burns in oxygen?
Ans: Due to weak covalent bonds
- Carbon dioxide and water are produced/
CH4 + 2O2à CO2 + 2H2O
21) Write the main difference between an acid and a base. With the help of suitable explain the term neutralization and the formation of-
Ans:
Acid |
Base |
1) An acid produces H+ ions in aqueous solution | A base produces OH– ions in aqueous solution |
2) Acids are sour in taste. | Bases are bitter in taste |
3) Acids change the colour of blue litmus to red. | Bases change the colour of red litmus to blue. |
- Neutralization – A reaction of an acid with a base to produce salt and water.
(i) acidic,
Ans: NH4OH + HClàNH4Cl + H2O
(ii) basic
Ans: NaOH + H2CO3àNa2CO3 + H2O
and
(iii) neutral salts
Ans: KOH + HNO3àKNO3 + H2O
SECTION-E
22) In the experimental set up to show that “CO2 is given out during respiration”, name the substance taken in the small test tube kept in the conical flask. State its function and the consequence of its use.
Ans:
- Substance taken: KOH
- Function: It absorbs CO2 produced by the germinating seeds Consequence: The water level rises in the test tube dipped in the beaker / partial vacuum is created.
23) A student is observing the temporary mount of leaf peel under a microscope. Draw labelled diagram of the structure of stomata as seen under the microscope.
Ans:
OR
Draw a labelled diagram in proper sequence to show budding in hydra.
Ans:
24) List four precautions which a student should observe while determining the focal length of a given convex lens by obtaining image of a distant object on a screen.
Ans: Precautions:
1) Lens should be held in vertical position with its faces parallel to the screen
2) Clear and sharpest image should be obtained by adjusting the position of lens
3) Three observations should be taken at least.
4) Base of lens, screen and measuring scale should be in straight line
25) While studying the dependence of potential difference (V) across a resistor on the current (i) passing through it, in order to determine the resistance of the resistor, a student took 5 readings for different values of current and plotted a graph between V and I. He got a straight line graph passing through the origi8n. What does the straight line signify? Write the method of determining resistance of the resister using this graph.
Ans:
- Potential difference (V) is directly proportional to current (I) or V∝I
- Method: Finding slope of the graph
OR
What would you suggest to a student if while if while performing an experiment he finds that the pointer/ needle of the ammeter and voltmeter do not coincide with the zero marks on the scales when circuit is open? No extra ammeter/ Voltmeter is available in the laboratory.
Ans:
- Measure the zero error
- Value of zero error should be adjusted to the observed values
26) In three test tube A, B, and C, three different liquids namely, distilled water, underground water and distilled water in which a pinch of calcium sulphate is added to each test tube and the contents are shaken. In which test tube will the length of the foam (lather) be longest? Justify your answer.
Ans:
- In test tube A
- As distilled water contains no salts
27) Blue litmus solution is added to two test tubes A and B containing dilute HCI and NaOH solution respectively. In which test tube a colour change will be observed? State the colour change and give its reason.
Ans:
- Test Tube A
- It changes the colour from blue to red Hydrochloric acid turns blue litmus red.
OR
What is observed when 2 ml of dilute hydrochloric acid is added to 1 g of sodium carbonate taken in a clean and dry test tube? Write chemical equation for the reaction involved.
Ans:
- Brisk effervescence is produced
Na2CO3 + 2HClà 2 NaCl + H2O + CO2
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)