CBSE Class 10 Science Previous Question Paper 2019 Solution
SCIENCE
SECTION-A
1) What is the function of a galvanometer in a circuit?
Ans: Detect the presence or direction of current.
2) Why is biogas considered an excellent fuel?
Ans: It burns completely/ burns without smoke / high calorific value.
SECTION-B
3) 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
4) Write two different ways in which glucose is oxidized to provide energy in human body. Write the products formed in each case.
Ans:
- Aerobic / Presence of oxygen
Product – CO2 and H2O
- Anaerobic / Absence of oxygen
Product – lactic acid
5) Define the term power of accommodation. Write the modification in the curvature of the eye lens which enables us to see the nearby objects clearly?
Ans:
- Power of accommodation – Ability of eye lens to adjust its focal length.
- Curvature increases/lens becomes thick
SECTION-C
6) 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
7) Identify the acid and the base from which sodium chloride is obtained. Which type of salt is it ? When is it called rock salt formed?
Ans:
- Acid – Hydrochloric acid/HCl Base – Sodium hydroxide/NaOH
- Neutral Salt
- When it forms brown crystals combined with impurities
- Drying up of seas
8) 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.
9) Write three types of blood vessels. Give one important feature of each.
Ans:
- Arteries – No valves/thick walled/carry oxygenated blood/carry blood away from heart.
- Veins – Presence of valves/thin walled/carry deoxygenated blood/carry blood towards heart.
- Capillaries – very fine/mixed blood/found in tissues/sites for material exchange.
10) Trace the sequence of events which. Occur when a bright light is focused on your eyes.
Ans: Receptor Cells of eyes/retinaà Sensory Neuronà Brain / CNS Pupil contracts / Eye lids close/blinkß Eye Muscles ß Motor Neuron
11) What are plant hormones? Name the plant hormones responsible for the following:
Ans: Plant hormones – Chemical substances which help the plant to coordinate growth and development
(i) Growth of stem
Ans: Auxins/ Gibberellins
(ii) promotion of cell division
Ans: Cytokinins
(iii) Inhibition of growth
Ans: Abscisic Acid / ABA
(Iv) Elongation of cells
Ans: Auxins/ Gibberellins
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) 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
14) How can we help in reduci8ng 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.
15)What is water harvesting? List two main advantages associated with water harvesting at the community level. Write two causes for the failure of sustained availability of groundwater.
Ans:
- A technique used to collect and store water for future use
- Advantages – Available resource in time of need Recharging the ground water level
- Causes – Overuse of ground water Deforestation
SECTION-D
16)(a) List in tabular from three chemical properties on the basis of which we can differentiate between a metal and a non-metal.
Ans:
Metals |
Non Metals |
Metals form basic oxides with oxygen | Non – metals form acidic or neutral oxides with oxygen |
Metals react with dilute acids to liberate hydrogen | Non metals do not displace hydrogen from dilute acids |
Metals form positively charged ions by losing electrons | Non metals form negatively charged ions by gaining electrons |
(b) Give reasons for the followi8ng:
(i) Most metals conduct electricity well.
Ans: Metals have loosely bound electrons / Loose electrons easily / free electrons
(ii) The reaction of iron (III) oxide [Fe2O3] with heated aluminium is used to join cracked machine parts.
Ans: Molten iron produced during reaction joins the cracked machine parts.
17) 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
18) 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
19) 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:
20) 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
21) What is a solenoid? Draw the pattern of magnetic field lines of
Ans: A coil of many turns of insulated copper wire wrapped closely in the shape of a cylinder
(i) a current carrying solenoid and
ANS:
(ii) a bar magnet. list two distinguishing features between the two fields.
Ans:
Distinguishing features-
Solenoid |
Bar Magnet |
Field disappear on stopping the current | No effect of current on field. |
Strength of the field can be changed by changing the current | Strength cannot be changed |
Strength of the field can be changed by changing the current | Direction is fixed and cannot be reversed. |
SECTION-E
22) 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
23) 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
24) 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:
25) 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.
26) 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
27) 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
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)