CBSE Previous Year Question Papers

Class 10 Science 2019 Delhi

Time allowed: 3 hours
Maximum marks: 80

• The question paper comprises five sections, A, B, C, D and E. You are to attempt all the sections.

• All questions are compulsory.

• Internal choice is given in Sections B, C, D and E.

• Question number 1 and 2 in Section A are one mark questions. They are to be answered in one word or in one sentence.

• Questions number 3 to 5 in Section B are two marks questions. These are to be answered in about 30 words each.

• Questions number 6 to 15 in Section C are three-marks questions. These are to be answered in about 50 words each.

• Question number 16 to 21 in Section D are five-marks questions. These are to be answered in about 70 words each.

• Questions number 22 to 27 in Section E are based on practical skills. Each question is a two marks question. These are to be answered in brief.

CBSE Previous Year Question Papers Class 10 Science 2019 Delhi Set I

Section – A

Question 1.
What is the function of a galvanometer in a circuit? [1]
Answer:
Galvanometer is a device that detects the presence of current in a circuit. It is also used for measuring the amount of current in the circuit.

Question 2.
Why is biogas considered excellent fuel? [1]
Answer:
Biogas is considered as an excellent fuel because:

• It causes no pollution, as it is environmentally friendly.

• Biogas plant from which biogas is produced serves as an excellent way of waste disposal.

• It is economical and produces a large amount of heat per unit mass.

Section – B

Question 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?
OR
The electronic configuration of an element is 2, 8, 4. State its:
(a) group and period in the Modern Periodic Table.
(b) name and write its one physical property. [2]
Answer:
(a) Modern periodic law states that the physical and chemical properties of an element are a periodic function of the atomic number of that element.
Electronic configuration of the elements play an important role in the placement of elements in the modern periodic table. The valence shell electron of an element decides its position in a particular group or period for example: if the configuration of an element is 2, 1 it means that the
Li = 2, 1
It belongs to the 2nd period and 1st group.
OR
(b) Si = 2, 8, 4
1. It means that it belongs to the 3rd period and 14th group.
2. The name of the element is Silicon.
It is a metalloid, (i.e. element that has properties of both metals and nonmetals).

Question 4.
Write two different ways in which glucose is oxidized to provide energy in the human body. Write the products formed in each case. [2]
Answer:
Glucose is oxidised in two forms to provide energy to the body:

This is an example of Aerobic Respiration that happens in the presence of oxygen.

This is an example of Anaerobic Respiration.

Question 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? [2]
Answer:
The ability of the eye lens to adjust its focal length is called the power of accommodation. There should be a contraction . of ciliary muscles, that will increase the curvature of the eye lens and becomes thicker, so the focal length of the eye lens will decrease. It will thus enable us to see the objects clearly.

Section – C

Question 6.
2 g of silver chloride is taken in a china dish and the china dish is placed in sunlight for some time. What will be your observation in this case? Write the chemical reaction involved in the form of a balanced chemical equation. Identify the type of chemical reaction.
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 to produce zinc nitrate and silver.
(b) Potassium iodide reacts with lead nitrate to produce potassium nitrate and lead iodide. [3]
Answer:

Initially, the colour of silver chloride is white but when it is kept in sunlight it breaks down to give silver and chlorine. Hence, the colour changes to grey.
It is an example of Photo-Chemical Decomposition.
OR
(a) The given reaction is a displacement reaction.

(b) It is a double displacement reaction.

Question 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? How is rock salt formed? [3]
Answer:
NaCl is made by reacting an acid and a base. The base is NaOH (Sodium hydroxide). So,
HCl + NaOH → NaCl + H₂O
It is a Neutralization Reaction.
It is known as rock salt in crystalline form.
It is the result of the evaporation of ancient oceans millions of years ago. Sometimes pressure from deep inside the Earth forces up large masses of rocks to form salt-like domes.

Question 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.
(ii) Halide of the elements of group thirteen, and
(iii) Compound formed when an element, A of group 2 combines with an element, B of group seventeen. [3]
Answer:
(i) Sodium is a group one element (Na) so its configuration is 2, 8, 1 and its valency is 1.
Oxide has a valency of 2.
So their formula would be

Formula for sodium oxide is Na₂O.
(ii) Halide is any Halogen. Group 13 means, for example, we take Aluminium (Al) its configuration is 2, 8, 3, the valency of Al is 3, valency of Cl is 1 So,

Formula would be AlCl₃ (Aluminium chloride)
(iii) Element of group 2, for example, Mg 2, 8, 2 its valency would be 2.
Element of group 17 would be Cl 2, 8, 7 valency would be 1.

Formula would be MgCl₂ – (Magnesium Chloride)

Question 9.
Write three types of blood vessels. Give one important feature of each. [3]
Answer:
The three types of blood vessels are:

1. Arteries: They carry oxygenated blood from the heart and transport it to organs.

2. Veins: They carry deoxygenated blood from organs and take this blood to the heart.

3. Capillaries: Arteries and veins divide to form arterioles and venules. The nutrients, hormones and gases can diffuse into the tissue cells through the walls of capillaries and vice versa.

Question 10.
Trace the sequence of events which occur when a bright light is focused on your eyes. [3]
Answer:
When bright light is focussed on our eyes it goes to the brain, the brain reverts back the message by motor neuron which contracts the pupil. The sequence of events which occur is as follows:

Question 11.
What are plant hormones? Name the plant hormones responsible for the following:
(i) Growth of stem
(ii) Promotion of cell division
(iii) Inhibition of growth
(iv) Elongation of cells [3]
Answer:
In plants, growth, development and response to the environment are controlled and coordinated by a special class of chemical substances known as phytohormones. They are synthesised in minute amounts.
(i) Gibberellins
(ii) Cytokinins
(iii) Abscisic acid
(iv) Auxins

Question 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? Write the ratio he obtained in F2 generation plants.
OR
List two differences between acquired traits and inherited traits by giving an example of each. [3]
Answer:
Mendel used pea plant (Pisum sativum) when he crossed tall and short plants the progeny obtained in FI generation were tall. When the F1 plants were selfed F2 generations showed three tall and one dwarf plants. The phenotypic ratio of the F2 generation is 1 : 2 : 1 (TT : Tt : Tt : tt)
The phenotypic ratio is 3 : 1 (Tall : Dwarf)

Question 13.
What is a rainbow? Draw a labelled diagram to show the formation of a rainbow. [3]
Answer:
The Rainbow is a natural phenomenon in which the white light or sunlight splits into beautiful 7 colours by the water droplets which remain suspended in the air after rain.

Question 14.
How can we help in reducing the problem of waste disposal? Suggest any three methods.
OR
Define an ecosystem. Draw a block diagram to show the flow of energy in an ecosystem. [3]
Answer:
The three methods by which we can reduce the problem of waste disposal are:
1. Adopting the 3R approach i.e;-Reduce, Reuse, Recycle.
2. Segregation of waste into biodegradable and non-biodegradable waste.
3. Conversion of waste into useful components like biogas and then using compost as a fertiliser.
OR
Ecosystem refers to the interaction of all the biotic and abiotic components present in a particular area. Energy flows across the trophic levels following the 10% law. Only 10% of the energy available to a trophic level is passed on to the next trophic level.

1. For example 10,000J energy is available to the producer.
2. Then 1000J energy will be available to the primary consumer.
3. 100J energy will be available to secondary consumer.
4. 10J energy will be available to tertiary consumers.

Question 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. [3]
Answer:
Water harvesting means capturing rain where it falls or capturing the runoff in village or town. It can be done by capturing runoff from rooftops and local catchments.
Advantages:

• Harvesting water allows capturing better utilization of an energy resource or when there is an immediate need.

• This water is suitable for irrigation.

Causes for failure of sustained groundwater availability are:

• Increase in agricultural activities leads to depletion of groundwater.

• Increase in population and industries are also responsible for the same.

Section – D

Question 16.
(a) List in tabular form three chemical properties on the basis of which we can differentiate between a metal and a nonmetal.
(b) Give reasons for the following:
(i) Most metals conduct electricity well.
(ii) The reaction of iron (III) oxide [Fe₂O₃] with heated aluminium is used to join cracked machine parts. [5]
Answer:

(b) (i) Metals, for example, Na has an electronic configuration of 2, 8, 1 i.e. It has one free electron. This electron moves through the metal and conduct electric current due to the presence of free electrons.
(ii) Fe₂O₃ (s) + 2Al (s) → Al₂O₃ (s) + 2Fe (l) + Heat
It is thermite reaction
This reaction is an exothermic reaction the reaction produces a large amount of heat due to which iron metal is produced in molten form and use to join the tracks.

Question 17.
Write the chemical formula and name of the compound which is the active ingredient of all alcoholic drinks. List its two uses. Write a chemical equation and name of the product formed when this compound reacts with
(i) sodium metal
(ii) hot concentrated sulphuric acid
OR
What is methane? Draw its electron dot structure. Name the type of bonds formed in this compound. Why are such compounds:
(i) poor conductors of electricity? and
(ii) have low melting and boiling points?
What happens when this compound burns in oxygen? [5]
Answer:
The name of the ingredient of the alcoholic drink is ethanol.
Its formula is C₂H₅OH.
Two uses of ethanol (C₂H₅OH) are:
1. It is used as a solvent in various industries.
2. It is also used as an antiseptic solution.
(i) Reaction of ethanol with sodium metal

(ii) Reaction of ethanol with conc. H₂SO₄

OR
Methane is a Hydrocarbon formed by the combination of carbon with Hydrogen.
Its molecular formula is CH₄. It is the main greenhouse gas. The type of bond formed in methane is a covalent bond.
Electron dot structure of methane (CH₄):

(i) Covalent compounds are poor conductors of electricity because it has no free electrons to conduct electricity. Moreover, this compound is formed by sharing of electrons. So no electron is available for conduction.
(ii) They have weak forces of attraction between them so less energy is required to break the force of binding. Thus they have low melting and boiling points. When this compound burns in oxygen, the combustion reaction takes place.

Question 18.
Define pollination. Explain the different types of pollination. List two agents of pollination? How does suitable pollination lead to fertilization?
OR
(a) Identify the given diagram. Name the parts 1 to 5.

(b) What is contraception? List three advantages of adopting contraceptive measures. [5]
Answer:
Pollination is the transfer of pollen from the anther of a stamen to the stigma of the pistil with the help of air, water and insects.
Types of pollination:

1. Self-pollination: Transfer of pollen grains from the anther to the stigma of the same flower.

2. Cross-pollination: Transfer of pollen grains from the anther of one flower to the stigma of other flowers of the same species.

Two agents of pollination are air, water, insects etc.
When correct species of pollen grain lands on the stigma it results in some chemical response from the ovary that causes the growth of pollen tube from pollen grain. The pollen grain slides down the pollen tube and enters the ovary where it meets the egg. This process is called fertilization and leads to the formation of zygote.
OR
The parts of the female Reproductive system are as follows:

1. Fallopian tube or Oviduct

2. Ovary

3. Uterus

4. Cervix

5. Vagina

Contraception is the method by which a female inhibits fertilization and hence presents pregnancy.
The three advantages of contraception are:

1. It makes people more aware of the concept of family planning.

2. It educates the people about Sexually Transmitted Diseases and ways to avoid it.

3. It helps the female to space children.

4. It reduces the risk of unwanted pregnancies.

Question 19.
An object is placed at a distance of 60 cm from a concave lens of focal length 30 cm.
(i) Use the lens formula to find the distance of the image from the lens.
(ii) List four characteristics of the image (nature, position, size, erect/inverted) formed by the lens in this case.
(iii) Draw ray diagram to justify your answer of the part (ii). [5]
Answer:

(ii) So, the image formed will be virtual, erect, small in size and image will be formed between F1 and O.

Question 20.
(a) 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 reciprocals of the individual resistances.
(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.
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,
(b) the current through the circuit,
(c) the potential difference across the (i) electric lamp and (ii) conductor, and
(d) power of the lamp. [5]
Answer:
(a) It is observed that total current I is equal to the sum of separate currents.
I = I₁ + I₂ + I₂₃ …(i)
Let Rp be the equivalent resistance of the parallel combination of resistors.

Question 21.
What is a solenoid? Draw the pattern of magnetic field lines of (i) a current-carrying solenoid and (ii) a bar magnet. List two distinguishing features between the two fields. [5]
Answer:
The solenoid is a long cylindrical coil of wire consisting of a large number of turns bound together very tightly.

Distinguishing features are as follows:

1. Magnetic field outside the solenoid is negligible as compared to the bar magnet.

2. Magnetic field of solenoid can be varied as per our requirement just by changing current or core of solenoid but in bar magnet it is fixed.

Section – E

Question 22.
Blue litmus solution is added to two test tubes A and B containing dilute HC1 and NaOH solution respectively. In which test tube a colour change will be observed? State the colour change and give its reason.
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 the chemical equation for the reaction involved. [2]
Answer:
Test tube A will show colour change because acids turn blue litmus red. So the final colour of the test tube would be red.
OR
A brisk effervescence would be observed if HCl is added to Na₂CO₃ due to the evolution of CO₂ gas.
Na₂CO₃ + HCl → NaCl + H₂O + CO₂.

Question 23.
In three test tubes A, B and C, three different liquids namely, distilled water, underground water and distilled water in which a pinch of calcium sulphate is dissolved, respectively are taken. An equal amount of soap solution 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. [2]
Answer:
Length of foam would be longest in test tube A. It is because it does not have any ions, so the length of the foam would be longest.

Question 24.
A student is observing the temporary mount of a leaf peel under a microscope. Draw a labelled diagram of the structure of stomata as seen under the microscope.
OR
Draw a labelled diagram in the proper sequence to show budding in hydra. [2]
Answer:

Question 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. [2]
Answer:
The chemical kept in the test tube is KOH-Potassium Hydroxide. The function of this chemical is to absorb the vapours of CO₂.

Question 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 origin. What does the straight-line signify? Write the method of determining the resistance of the resistor using this graph.
OR
What would you suggest to a student 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 the circuit is open? No extra ammeter/voltmeter is available in the laboratory. [2]
Answer:
The straight line in the graph signify that potential difference and current are directly proportional to each other.
The method of determining resistance of resistor using the graph is by Ohm’s law,
V = IR and by calculating the slope from the points mentioned on the graph

OR
This is called the zero error of the scale of ammeter or voltmeter. If there is a zero error then this error is subtracted from the value that depicts when the circuit is closed otherwise accurate readings will not be recorded.

Question 27.
List four precautions which a student should observe while determining the focal length of a convex lens by obtaining an image of a distant object on a screen. [2]
Answer:
Precautions are as follows:

• Fix the lens vertically in lens holder.

• Base of lens and white screen should be in line with measuring scale.

• There should not be any obstacle in path of lens.

• Record the position of lens and screen when sharp image is formed.