CBSE Class 10th Science Question Paper Solved 2017 18 19 20 With Solutions

Class 10 Subject Science Paper Set 4 with Solutions

---

Question 1: (Marks 1)

Write the number of valence electrons present in a nitrogen atom (₇¹⁴N).

---

Answer :

5 valence electrons

---

Question 2: (Marks 1)

Define the term induced electric current.

---

Answer :

The electric current generated /induced in a conductor by changing magnetic field around it.

---

Question 3: (Marks 4)

Around the year 1800, only 30 elements were known. Dobereiner in 1817 and Newlands in 1866 tried to arrange the then known elements and framed laws which were rejected by the scientists. Even after the rejection of the proposed laws, many scientists continued to search for a pattern that correlated the properties of elements with their atomic masses.

The main credit for classifying elements goes to Mendeleev for his most important contribution to the early development of a Periodic table of elements wherein he arranged the elements on the basis of their fundamental property, the atomic mass and also on the similarity of chemical properties. The formulae of their hydrides and oxides were treated as basic criteria for the classification of the elements.

However, Mendeleev’s classification also had some limitations as it could not assign the position to isotopes. He also left some gaps in the periodic table.

3(a) State Mendeleev’s Periodic Law. (Marks 1)

3(b) Why did Mendeleev leave some gaps in the Periodic table ? (Marks 1)

3(c) If the letter ‘R’ was used to represent any of the elements in the group, then the hydride and oxide of carbon would respectively be represented as (Marks 1)

(i) RH₄, RO

(ii) RH₄, RO₂

(iii) RH₂, RO₂

(iv) RH₂, RO

3(d) Isotopes are (Marks 1)

(i) Atoms of an element with similar chemical properties but different atomic masses.

(ii) Atoms of different elements with similar chemical properties but different atomic masses.

(iii) Atoms of an element with different chemical properties but same atomic masses.

(iv) Atoms of different elements with different chemical properties but same atomic masses.

---

Answer :

(a) The properties of elements are the periodic functions of their atomic masses.

(b) To fill with undiscovered elements.

(c) (ii)/RH₄, RO₂

(d) (i)/Atoms of an element with similar chemical properties but different atomic masses.

---

Question 4: (Marks 4)

India today is facing the problem of overuse of resources, contamination of water and soil and lack of methods of processing the waste. The time has come for the world to say goodbye to ‘‘single-use plastics’’. Steps must be undertaken to develop environment-friendly substitutes, effective plastic waste collection and methods of its disposal.

Indore treated 15 lakh metric tonnes of waste in just 3 years, through biomining and bioremediation techniques. Bioremediation involves introducing microbes into a landfill to naturally ‘break’ it down and biomining involves using trommel machines to sift through the waste to separate the ‘soil’ and the waste component. The city managed to chip away 15 lakh metric tonnes of waste at a cost of around < 10 crore. A similar experiment was successfully carried out in Ahmedabad also.

4(a) State two methods of effective plastic waste collection in your school. (Marks 1)

4(b) Name any two uses of ‘‘single-use plastic’’ in daily life. (Marks 1)

4(c) If we discontinue the use of plastic, how can an environment-friendly substitute be provided ? (Marks 1)

4(d) Do you think microbes will work similarly in landfill sites as they work in the laboratory ? Justify your answer. (Marks 1)

---

Answer :

(a) Use of separate bins for plastic and paper ; separation of biodegradable and non biodegradable wasteor any other.

(b)
► Packaging of articles like water, food, milk, biscuits etc.
► Disposable utility items –bowls, tumblers, plates , leaves etc.

(c) By providing cloth /jute /earthern pots and utensils/ paper or any other material for the similar purposes.

(d)
► Yes
► The action of microbes is tested in the laboratory creating the same conditions as in the landfill.

---

Question 5: (Marks 1)

Which one of the following statements is correct about the human circulatory system ?

(A) Blood transports only oxygen and not carbon dioxide.

(B) Human heart has five chambers.

(C) Valves ensure that the blood does not flow backwards.

(D) Both oxygen-rich and oxygen-deficient blood gets mixed in the heart.

---

Answer :

(C) / Valves ensure that the blood does not flow backwards.

---

Question 6: (Marks 1)

Anaerobic process

(A) takes place in yeast during fermentation.

(B) takes place in the presence of oxygen.

(C) produces only energy in the muscles of human beings.

(D) produces ethanol, oxygen and energy.

OR

Most of the digestion and absorption of the food takes place in the

(A) small intestine.

(B) liver.

(C) stomach.

(D) large intestine.

---

Answer :

(A)/ takes place in yeast during fermentation.

OR

(A)/ small intestine

---

Question 7: (Marks 1)

Fertilisation is the process of

(A) transfer of male gamete to female gamete.

(B) fusion of nuclei of male and female gamete.

(C) adhesion of male and female reproductive organs.

(D) the formation of gametes by a reproductive organ.

---

Answer :

(B) /fusion of nuclei of male and female gamete.

---

Question 8: (Marks 1)

---

Answer :

(A) /1 Ω

OR

(B) /half

---

Question 9: (Marks 1)

Fleming’s Right-hand rule gives

(A) magnitude of the induced current.

(B) magnitude of the magnetic field.

(C) direction of the induced current.

(D) both, direction and magnitude of the induced current.

---

Answer :

(C) /direction of the induced current

---

Question 10: (Marks 1)

Which one of the following statements is not true about nuclear energy generation in a nuclear reactor ?

(A) Energy is obtained by a process called nuclear fission.

(B) The nucleus of Uranium is bombarded with high energy neutrons.

(C) A chain reaction is set in the process.

(D) In this process a tremendous amount of energy is released at a controlled rate.

OR

The biggest source of energy on Earth’s surface is

(A) Biomass

(B) Solar radiations

(C) Tides

(D) Winds

---

Answer :

(B)/ The nucleus of Uranium is bombarded with high energy neutrons.

OR

(A)/ Biomass

---

Question 11: (Marks 1)

Food web is constituted by

(A) relationship between the organisms and the environment.

(B) relationship between plants and animals.

(C) various interlinked food chains in an ecosystem.

(D) relationship between animals and environment.

---

Answer :

(C) /various interlinked food chains in an ecosystem

---

Question 12: (Marks 1)

Choose the incorrect statement from the following :

(A) Ozone is a molecule formed by three atoms of oxygen.

(B) Ozone shields the surface of the Earth from ultraviolet radiations.

(C) Ozone is deadly poisonous.

(D) Ozone gets decomposed by UV radiations.

---

Answer :

Note: Treat all answers as correct. Give full credit even if not attempted.

---

Question 13: (Marks 1)

Assertion (A) : Following is a balanced chemical equation for the action of steam on iron :

3Fe + 4H2O → Fe3O4 + 4H2

Reason (R) : The law of conservation of mass holds good for a chemical equation.

---

Answer :

(b) /Both (A) and (R) are true but (R) is not the correct explanation of theassertion (A)

---

Question 14: (Marks 1)

Assertion (A) : The sex of a child in human beings will be determined by the type of chromosome he/she inherits from the father.

Reason (R) : A child who inherits ‘X’ chromosome from his father would be a girl (XX), while a child who inherits a ‘Y’ chromosome from the father would be a boy (XY).

---

Answer :

(a) /Both (A) and (R) are true and ( R) is the correct explanation of the assertion (A).

---

Question 15: (Marks 3)

Lead nitrate solution is added to a test tube containing potassium iodide solution.

(a) Write the name and colour of the compound precipitated.

(b) Write the balanced chemical equation for the reaction involved.

(c) Name the type of this reaction justifying your answer.

OR

What happens when food materials containing fats and oils are left for a long time ? List two observable changes and suggest three ways by which this phenomenon can be prevented.

---

Answer :

(a) Lead iodide; Yellowcolour

(b) Pb(NO₃)₂ + 2 KI → PbI₂ + 2KN0₃

Note : ½ marks to be deducted if reaction is not balanced.

(c) Double displacement reaction ; Due to exchange of ions.

OR

► Fats and oils become rancid.

► Observable changes –
1. Change in taste
2. Change in smell

► Three ways of prevention :-
i) Addition of antioxidants / substance which prevent oxidation.
ii) Keeping food in air tight containers.
iii) Use of nitrogen gas in packaged food

---

Question 16: (Marks 3)

List three differentiating features between the processes of galvanisation and alloying.

OR

Compare in tabular form the reactivities of the following metals with cold and hot water :

(a) Sodium

(b) Calcium

(c) Magnesium

---

Answer :

OR

---

Question 17: (Marks 3)

Carbon, a member of group 14, forms a large number of carbon compounds estimated to be about three million. Why is this property not exhibited by other elements of this group ? Explain.

---

Answer :

► Carbon atom, the first member of group 14 has the smallest size in the group and highest inter-atomic force of attraction.

► It has four valence electrons and requires four more electrons to attain stable configuration.

► Due to its small size, nucleus of carbon is able to hold the shared pairs of electrons strongly.

► The bonds formed by other elements of the same group are weaker due to bigger size of their atoms. (Any Three)

---

Question 18: (Marks 3)

A cheetah, on seeing a prey, moves towards him at a very high speed. What causes the movement of his muscles ? How does the chemistry of cellular components of muscles change during this event ?

---

Answer :

► A cheetah on seeing a prey generates a nerve impulse which reaches the muscles and the muscle fibre moves. The muscle cell will then move by changing their shape so that muscle cells shorten.

► Muscle cells have special proteins that change both shape and their arrangement in the cell in response to nervous electrical impulses.

When this happens new arrangements of these proteins give the muscle cells a shorter form.

---

Question 19: (Marks 3)

Define geotropism. Draw a labelled diagram of a plant showing geotropic movements of its parts.

---

Answer :

The movement of the growth of the roots downwards and the shoots upwards under the stimuli of gravity is called geotropism./ The movement of the part of the plant towards or away from the stimulus gravity

---

Question 20: (Marks 3)

Define the term evolution. ‘‘Evolution cannot be equated with progress.’’ Justify this statement.

OR

‘‘During the course of evolution, organs or features may be adapted for new functions.’’ Explain this fact by choosing an appropriate example.

Answer :

► Evolution – Gradual change in living organisms with time since the beginning of life resulting in the formation of a new species/ Evolution is simply the generation of diversity and the shaping of diversity by environmental selection.

► Evolution cannot be equated with progress because more and more complex body designs have emerged and evolved over time but this does not mean that older designs are inefficient.Foreg. Bacteria are simpler organisms but some inhabit the most inhospitable habitats like hot springs, deep sea, thermal vents and the ice in Antartica.

OR

Examples of feathers :
- Feathers can start out as providing insulation in cold weather but later they might become useful for flight.
- Some dinosaurs have feathers but they could not fly.
- Birds later adapted the feathers for flight .
- This shows that birds are closely related to reptiles.

---

Question 21:(Marks 3)

A concave mirror is used for image formation for different positions of an object. What inferences can be drawn about the following when an object is placed at a distance of 10 cm from the pole of a concave mirror of focal length 15 cm ?

(a) Position of the image

(b) Size of the image

(c) Nature of the image

Draw a labelled ray diagram to justify your inferences.

Answer :

(a) Behind the mirror

(b) Magnified

(c) Virtual and erect

Labelled ray diagram

---

Question 22: (Marks 3)

The refractive index of a medium ‘x’ with respect to a medium ‘y’ is 2/3 and the refractive index of medium ‘y’ with respect to medium ‘z’ is 4/3. Find the refractive index of medium ‘z’ with respect to medium ‘x’. If the speed of light in medium ‘x’ is 3 × 10⁸ ms⁻¹, calculate the speed of light in medium ‘y’.

Answer :

---

Question 23: (Marks 3)

A person may suffer from both myopia and hypermetropia defects.

(a) What is this condition called ?

(b) When does it happen ?

(c) Name the type of lens often required by the persons suffering from this defect. Draw labelled diagram of such lenses.

---

Answer :

(a) Presbyopia

(b) Gradual weakening of the ciliary muscles of the eye/ diminishing flexibility of the eye lens.

(c) Bifocal lens

---

Question 24: (Marks 3)

How will you use two identical glass prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light ? Draw and label the ray diagram.

---

Answer :

By placing second (identical) prism in an inverted position with respect to the first prism.

---

Question 25: (Marks 5)

A cloth strip dipped in onion juice is used for testing a liquid ‘X’. The liquid ‘X’ changes its odour. Which type of an indicator is onion juice ? The liquid ‘X’ turns blue litmus red. List the observations the liquid ‘X’ will show on reacting with the following :

(a) Zinc granules

(b) Solid sodium carbonate Write the chemical equations for the reactions involved.

OR

Define water of crystallisation. Give the chemical formula for two compounds as examples. How can it be proved that the water of crystallisation makes a difference in the state and colour of the compounds ?

---

Answer :

Olfactory indicator

(a) Colourless and Odourless gas is evolved with bubbles.

Zinc + Acid → ZincSalt + H₂

( or by using any example of acid e.g. HCl/ H₂SO₄)↑

(b) Brisk effervescence/ colourless and odourless gas is evolved.

Sodium carbonate + Acid → Sodium salt of Acid + Water + Carbon dioxide↑

( or by using any example of acid like HCl/ H₂SO₄)

OR

► Water of crystallization is the fixed number of water molecules present in one formula unit of a salt.

► Examples CuSO₄ .5H₂O
Na₂CO₃.10 H₂O ( or Any other)

► Heat a few crystals of hydrated copper sulphate( bluecolour) in a dry boiling tube.

Water droplets are seen in the boiling tube.

Colour : The colour of copper sulphate changes to white .
State : The blue crystal changes to white powder.

---

Question 26: (Marks 5)

(a) (i) Write two properties of gold which make it the most suitable metal for ornaments.
(ii) Name two metals which are the best conductors of heat.
(iii) Name two metals which melt when you keep them on your palm.

(b) Explain the formation of ionic compound CaO with electron-dot structure. Atomic numbers of calcium and oxygen are 20 and 8 respectively.

---

Answer :

(a)(i) Ductility / Malleability / Lusture ( Any two)
(ii) Silver , Copper
(iii) Gallium, Caesium

---

Question 27: (Marks 3)

(a) Why is nutrition necessary for the human body ?

(b) What causes movement of food inside the alimentary canal ?

(c) Why is small intestine in herbivores longer than in carnivores ?

(d) What will happen if mucus is not secreted by the gastric glands ?

---

Answer :

(a) For providing energy for various metabolic processes / Formation of new cells / Repair of damaged or worn out cells & tissues / Developing resistance against diseases. (Any Two)

(b) Peristaltic movement / Peristalsis/ Rhythmic contraction and relaxation of the muscles in the lining of alimentary canal.

(c) Herbivores eat plant matter which is rich in cellulose and takes longer time to digest and hence longer small intestine.

(d) The inner lining of the stomach will not be protected from the action of the acid /HCl

---

Question 28: (Marks 5)

Draw a neat diagram showing fertilisation in a flower and label (a) Pollen tube, (b) Male germ cell and (c) Female germ cell, on it. Explain the process of fertilisation in a flower. What happens to the (i) ovary and (ii) ovule after fertilisation ?

OR

(a) What is puberty ?

(b) Describe in brief the functions of the following parts in the human male reproductive system :
(i) Testes
(ii) Seminal vesicle
(iii) Vas deferens
(iv) Urethra

(c) Why are testes located outside the abdominal cavity ? (d) State how sperms move towards the female germ cell.

---

Answer :

► Process of fertilization :
Pollen tube is formed from the pollen grain.
Fusion of male germ cell with female germ cell to form zygote.

► Ovary- Changes into fruit

► Ovule- Changes into Seed

OR

(a) The period during adolescence is called puberty/age of males and females at which reproductive organs become functional.

(b) (i) Testes – Production of sperms /Secretion of male sex hormone testosterone.
(ii) Seminal vesicle – secretes a fluid which makes the transport of sperms easier/ the fluid secreted gives nutrition to sperms.
(iii) Vas deferens- carries the sperms to the seminal vesicle.
(iv) Urethra- forms a common passage for both the sperms and urine. (Any one)

(c) Because the sperm formation requires a lower temperature than the normal body temperature.

(d) With the help of a long tail.

---

Question 29: (Marks 5)

Draw a schematic diagram of a circuit consisting of a battery of 3 cells of 2 V each, a combination of three resistors of 10 Ω, 20 Ω and 30 Ω connected in parallel, a plug key and an ammeter, all connected in series.

Use this circuit to find the value of the following :

(a) Current through each resistor (b) Total current in the circuit

(c) Total effective resistance of the circuit

OR

Two identical resistors, each of resistance 15

, are connected in (i) series, and (ii) parallel, in turn to a battery of 6 V. Calculate the ratio of the power consumed in the combination of resistors in each case.

---

Answer :

---

Question 30: (Marks 5)

(a) State Fleming’s Left-hand rule.

(b) List three characteristic features of the electric current used in our homes.

(c) What is a fuse ? Why is it called a safety device ?

(d) Why is it necessary to earth metallic electric appliances ?

---

Answer :

(a)Flemings’ Left hand rule:
Stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the forefinger points in the direction of magnetic field, middle finger in the direction of current , then the thumb will point in the direction of motion or force acting on the conductor.

(b) Three charactersticfeatures :
► Reverses direction periodically.

► Frequency of 50 Hz.
► Potential difference between live wire and netural wire is about 220V.

(c) ► Fuse is a safety device used in a circuit (or appliance) to prevent damage due to overloading/ short circuiting.
► It protects the circuit ( or appliance) by stopping the flow of any unduly high electric current / If current larger than the specified valueflows through the circuit , due to Joule’s heating effect the fuse wire melts and breaks the circuit.

(d) It provides a low resistance conducting path for the current and protects the user from electric shock due to leakage of current.

CBSE Class 10th Science Question Paper Solved 2017 18 19 20 with solutions

class 10 Science sample paper 2020 solved, sample paper class 10 Science, cbse class 10 Science question paper 2018, sample paper class 10 Science 2019, Science question paper for class 10, cbse previous year question papers class 10 Science, cbse sample paper for class 10 Science, cbse class 10 Science question paper 2019, class 10 Science sample paper 2019 solved, cbse class 10th Science question paper, 10th Science question paper, sample paper class 10 Science 2020, Science sample paper class 12, cbse question paper for class 9 Science, cbse Science sample paper, cbse 10th class Science

Ncert Solution for class 6 to 12 download in pdf