CBSE Class 10 Science Term 1 Exam 2021-22: Check Important Assertion Reason Questions with Answer Key

CBSE Class 10 Science Term 1 Exam 2021-22: After the Social Science paper, next major paper for Class 10 students will be of Science. CBSE Class 10 Science Term 1 Paper 2021 will be held on 2nd December. We have provided here some very important assertion-reason questions for Class 10 Science. You can read the chapter-wise questions to prepare for your Science paper. All the questions are prepared by experienced teachers. Answer Key for all questions is also provided. So, practice these important MCQs to score well in the CBSE Class 10 Science Paper 2021-22 (Term 1).  

CBSE Class 10 Science Assertion-Reason Questions (Chapter-wise)

Chapter 1 – Chemical Reactions And Equations

In the following questions, a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as: 

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

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

(c) A is true but R is false.

(d) A is false but R is true.

Also Check: CBSE Class 10 Science Best Resources for Quick Revision and Full Marks In Term 1 Paper

1.Assertion (A) : Decomposition of vegetable matter into compost is an example of exothermic reactions.

Reason (R) : Exothermic reaction are those reactions in which heat is evolved.

2.Assertion (A) : When HCl is added to zinc granules, a chemical reaction occurs.

Reason (R) : Evolution of a gas and change in colour indicate that the chemical reaction is taking place.

3.Assertion (A) : Calcium carbonate when heated gives calcium oxide and water.

Reason (R) : On heating calcium carbonate, decomposition reaction takes place.

4.Assertion (A) : Brown fumes are produced when lead nitrate is heated.

Reason (R) : Nitrogen dioxide gas is produced as a by product due to the decomposition of lead nitrate.

5.Assertion (A) : White silver chloride turns grey in sunlight.

Reason (R) : Decomposition of silver chloride in presence of sunlight takes place to form silver metal and chlorine gas.

6.Assertion (A): Pungent smelling gas is produced when sulphur burns in air.

Reason (R) : Sulphur trioxide is formed on reaction of sulphur with oxygen.

7.Assertion (A) : In a reaction of copper with oxygen, copper serves as a reducing agent.

Reason (R) : The substance which gains oxygen in a chemical reaction acts as a reducing agent.

8.Assertion (A) : In electrolysis of water, the volume of hydrogen liberated is twice the volume of oxygen ……formed.

Reason (R) : Water (H,0) has hydrogen and oxygen in the ratio of 1:2 by volume.

9.Assertion (A): Corrosion of iron is commonly known as rusting.

Reason (R) : Corrosion of iron occurs in presence of water and air.

10.Assertion (A) : The balancing of chemical equations is based on law of conservation of mass.

Reason (R) : Total mass of reactants is equal to total mass of products.

11.Assertion (A): In a balanced chemical equation, total mass of the reactants is equal to the total mass of the ……..products.

Reason (R): Mass can neither be created nor destroyed during a chemical change.

12.Assertion (A): Iron articles are painted so as to prevent them from rusting.

Reason (R): When the surface of iron is coated with paint, its surface does not come in contact with oxygen and moisture therefore rusting does not take place.

13.Assertion (A) : Chemical reaction changes the physical and chemical state of a substance.

Reason (R) : When electric current is passed through water (liquid), it decomposes to produce hydrogen and

oxygen gases.

14.Assertion (A): When calcium carbonate is heated, it decomposes to give calcium oxide and carbon dioxide.

Reason (R): The decomposition reaction takes place on application of heat, therefore, it is an endothermic reaction.

15.Assertion (A): Zinc reacts with sulphuric acid to form zinc sulphate and hydrogen gas and it is a displacement reaction.

Reason (R): Zinc reacts with oxygen to form zinc oxide.

16.Assertion (A): Chips manufacturers usually Ilush bags of chips with gas such as nitrogen to prevent the chips from getting oxidised.

Reason (R): This increase the taste ot the chips and helps in their digestion.

17.Assertion (A): Exposure of silver chloride to sunlight for a long duration turns grey due to the formation of silver by decomposition of silver chloride.

Reason (R): In this process, sublimation of silver chloride takes place.

18.Assertion (A): Rusting of iron metal is the most common form of corrosion.

Reason (R): The effect of rusting of iron can be reversed if they are left open in sunlight.

19.Assertion (A): AgBr is used on photographic and X-ray film.

Reason (R): AgBr is photosensitive and changes to Ag and bromine in presence of sunlight and undergoes decomposition reaction.

20.Assertion (A): Magnesium ribbon keeps on burning in atmosphere of nitrogen.

Reason (R) : Magnesium reacts with nitrogen to form magnesium nitride and this reaction is combination reaction.

Answer Key:

Q. No.

Answer

Q. No.

Answer

1

a

11

a

2

b

12

a

3

d

13

b

4

a

14

b

5

a

15

b

6

c

16

c

7

a

17

c

8

c

18

c

9

b

19

a

10

a

20

a

Also Check: CBSE Important Practice Questions for Class 10 Science Term 1 Exam (By CBSE Board)

Chapter 2 – Acids, Bases And Salts

In the following questions, a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as:

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

(b) Both assertion (A) and reason (R) are true but reason (R) is not the correct explanation of assertion (A).

(c) If Assertion is true, but Reason is false.

(d) If Assertion is false, but Reason is true.

1.Assertion : While dissolving an acid or base in water, the acids must always be added slowly to water with constant stirring.

Reason : Dissolving an acid or a base in water is highly exothermic reaction.

2.Assertion : On adding H2SO4 ,aqueous solution get corrosive

Reason : Hydronium ions are responsible for corrosive action.

3.Assertion : Phenolphthalein gives pink colour in basic solution.

Reason : Phenolphthalein is a natural indicator.

4.Assertion : HCl gas does not change the colour of dry blue litmus paper.

Reason : HCl gas dissolves in the water present in wet litmus paper to from H+ ions.

5.Assertion : HCl produces hydronium ions (H3O+) and chloride ions (Cl-) in aqueous solution.

Reason : In presence of water, bases give H+ ions.

6.Assertion : H2CO3 is a strong acid.

Reason : A strong acid dissociates completely or almost completely in water.

7.Assertion : Sodium hydroxide reacts with zinc to produce hydrogen gas.

Reason : Acids reacts with active metals to produce hydrogen gas.

8.Assertion : Salts are the products of an acid-base reaction.

Reason : Salt may be acidic or basic.

9.Assertion : Ammonia solution is an alkali.

Reason : Ammonia solution turns blue litmus paper red.

10.Assertion : Weak acids have low electrical conductivity.

Reason : Strong acids and weak acids have concentration of hydrogen ions in their solutions.

11.Assertion :Baking soda creates acidity in the stomach.

Reason : Baking soda is alkaline.

12.Assertion : During electrolysis of concentrated aqueous solution of sodium chloride, hydrogen gas produced at anode and chlorine gas is produced at cathode.

Reason : Ions get attracted to oppositely charged electrodes

13.Assertion : To dilute, concentrated sulphuric acid, acid is added to the water slowly.

Reason : A lot of heat energy will be given out in the dilution of concentrated sulphuric acid.

14.Assertion : Pure water is neither acidic nor basic.

Reason : The pH of a solution is inversely proportional to the concentration of hydrogen ions in it.

15.Assertion : When common salt is kept open, it absorbs moisture from the air.

Reason : Common salt contains magnesium chloride

16.Assertion : Gas bubbles are observed when sodium carbonate is added to dilute hydrochloride acid

Reason : Carbon dioxide is given off in the reaction.

17.Assertion : pH of ammonium chloride solution is in acidic range.

Reason : Solution of a salt of weak base and strong acid is acidic

18.Assertion : When zinc is added to dilute hydrochloric acid, hydrogen is given off.

Reason : Hydrogen chloride molecules contain hydrochloric acid and hydrogen atoms.

19.Assertion : H3PO4 and H2SO4 are known as polybasic acids.

Reason : They have two or more than two protons per molecule of the acid.

20.Assertion: If the pH inside the mouth decreases below5.5, the decay of tooth enamel begins.

Reason : The bacteria present in mouth degrades the sugar and left over food particles and produce acids that remains in the mouth after eating. Acid produced reacts with tooth enamel and erodes it.

Answer Key:

Q. No.

Answer

Q. No.

Answer

1

a

11

d

2

a

12

d

3

c

13

a

4

a

14

b

5

c

15

a

6

d

16

a

7

b

17

a

8

b

18

b

9

c

19

a

10

c

20

a

Chapter 3 – Metals And Non-Metals

In the following questions, a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as: 

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

(6) Both A and R are true, but R is not the correct explanation of the assertion.

(c) A is true, but R is false.

(d) A is false, but R is true.

1.Assertion : Different metals have different reactivities with water and dilute acids.

Reason: Reactivity of a metal depends on its position in the reactivity series.

2.Assertion: Iron is the most widely used metal. But it is never used in its pure state.

Reason: Pure iron is very soft and stretches easily when hot.

3.Assertion: Gold occurs in native state.

Reason: Gold is a reactive metal.

4.Assertion: The property of beating a metal into sheets is called ductility.

Reason: Gold and silver are most malleable metals.

5.Assertion: Silver and gold do not react with oxygen even at high temperatures.

Reason: Silver and gold are less active metals.

6.Assertion: The oxides of sulphur and phosphorus are acidic in nature.

Reason: Metal oxides are basic in nature.

7.Assertion: Bromine cannot displace chlorine from its salt solution.

Reason: Chlorine is more reactive than bromine.

8.Assertion: MgO exists in liquid state.

Reason: The electrostatic forces of attraction between Mg2+ and O2- ions constitute ionic bond.

9.Assertion: On reacting with water, calcium starts floating over water.

Reason: Calcium reacts with cold water at room temperature.

10.Assertion: The arrangement of metals in order of decreasing reactivities is called reactivity series.

Reason: Metals at the top of series are very reactive and metals at the bottom are least reactive.

11.Assertion: Non-metals are electronegative in nature.

Reason: They have tendency to lose electrons.

12.Assertion: lonic compounds have high melting and boiling points.

Reason: A large amount of energy is required to break the strong inter-ionic attraction in ionic compounds.

13.Assertion: Metals in general have very high melting and boiling points.

Reason: Metals have the strongest chemical bonds which are metallic in nature.

14.Assertion : Electrovalency of Na is +1.

Reason: The number of electrons which an atom either loses or gains in the formation of an ionic bond is known as its valency.

15.Assertion : Metals generally act as reducing agents.

Reason: The reducing character is expressed in terms of electron releasing tendency.

16.Assertion: Magnesium reacts with oxygen upon heating and burns brightly to form magnesium oxide.

Reason: Magnesium oxide is basic in nature.

17.Assertion: The reaction of calcium with water is less violent in comparison to that of sodium.

Reason: The heat evolved is not sufficient for the hydrogen to catch fire.

18.Assertion: C and N do not react with dil. HCl and dil. H2SO4 

Reason: Metals do not react with dil.HCl and dil. H2SO4 

19.Assertion: Copper displaces silver from silver nitrate solution.

Reason: Copper is more reactive than silver.

20.Assertion: Aluminum oxide and zinc oxide are acidic in nature.

Reason: Amphoteric nature means that substance have both acidic and basic character.

Answer Key:

Q. No.

Answer

Q. No.

Answer

1

a

11

c

2

a

12

a

3

c

13

a

4

d

14

a

5

a

15

b

6

b

16

b

7

a

17

a

8

d

18

c

9

b

19

a

10

b

20

d

Chapter 6 – Life Processes

In the following questions, a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as: 

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

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

(c) A is true but R is false.

(d) A is false but R is true.

1.Assertion (A) : Bile is essential for digestion of lipids.

Reason (R): Bile juice contains enzymes.

2.Assertion (A): The purpose of making urine is to filter out undigested food from the intestine.

Reason (R): Kidney filter the wastes and produce urine.

3.Assertion (A): Raw materials needed for photosynthesis are carbon dioxide, water and minerals.

Reason (R): Nutrients provide energy to an organism.

4.Assertion (A): Lungs always contain a residual volume of air.

Reason (R): It provides sufficient time for oxygen to be absorbed and for carbon dioxide to be released.

5.Assertion (A): Arteries are thick-walled and elastic in nature.

Reason (R): Arteries have to transport blood away from the heart.

6.Assertion (A): The movement of water and dissolved salts in xylem is always upwards.

Reason: ‘The upward movement of water is due to low pressure created by transpiration.

7.Assertion (A): The muscular walls of ventricles are thicker than auricles.

Reason (R): This helps in preventing the back flow of blood.

8.Assertion (A): Most of the living organisms carry out aerobic respiration.

Reason (R): Mitochondria is the site of aerobic respiration in the cell.

9.Assertion (A): Most of the living organisms carry out aerobic respiration.

Reason (R): Mitochondria is the site of aerobic respiration in the cell.

10.Assertion (A): Blood pressure is an arterial blood pressure.

Reason (R): It is measured by sphygmomanometer.

11.Assertion (A): Alveoli contains an extensive network of blood vessels.

Reason (R): Alveoli is the site where exchange of gases occur.

12.Assertion (A): Excretion is the biological process by which harmful wastes are removed from an organism’s body.

Reason (R): The mode of excretion is same in both in unicellular and multicellular organisms.

13.Assertion (A): In plants there is no need of specialised respiratory organs.

Reason (R): Plants do not have great demands of gaseous exchange.

14.Assertion (A): The inner lining of the small intestine has numerous finger-like projections called villi.

Reason (R): The villi increase the surface area for absorption.

15.Assertion (A): The accumulation of lactic acid in the muscles causes muscle cramps.

Reason (R): During vigorous physical exercise leg muscles respire anaerobically. 76

16.Assertion (A): Valves are present in the arteries.

Reason (R): Arteries carry oxygenated blood from the heart to different body parts except pulmonary artery.

17.Assertion (A): Diffusion does not meet high energy requirements of multi-cellular organisms

Reason (R) : Diffusion is a fast process but occurs at the surface of the body.

18.Assertion (A): Rings of cartilage are present in the throat.

Reason (R) : These ensure that the air-passage does not collapse.

19.Assertion (A): In woody plants gaseous exchange takes place through lenticels.

Reason (R) : Lenticels are specialised cells found along with stomata on the stem of woody plants.

20.Assertion (A): In human beings, the respiratory pigment is haemoglobin

Reason (R) : It is a type of protein which has high-affinity for carbon dioxide.

Answer Key:

Q. No.

Answer

Q. No.

Answer

1

c

11

a

2

d

12

c

3

b

13

a

4

a

14

a

5

b

15

a

6

a

16

d

7

c

17

c

8

b

18

a

9

c

19

c

10

b

20

c

Chapter 10 – Light  Reflection And Refraction

In the following questions, a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as: 

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

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

(c) A is true but R is false.

(d) A is false but R is true. 

1.Assertion (A) : A ray passing through the centre of curvature of a concave mirror after reflection, is reflected back along the same path.

Reason (R) : The incident rays fall on the mirror along the normal to the reflecting surface.

2.Assertion (A) : Light does not travel in the same direction in all the media.

Reason (R) : The speed of light does not change as it enters from one transparent medium to another.

3.Assertion (A) : The Centre of curvature is not a part of the mirror. It lies outside its reflecting surface.

Reason (R): The reflecting surface of a spherical mirror forms a part of a sphere. This sphere has a Centre.

4.Assertion (A): The emergent ray is parallel to the direction of the incident ray in case of a glass slab.

Reason (R): The extent of bending of the ray of light at the opposite parallel faces (air- glass interface and glass-air interface) of the rectangular glass slab is equal and opposite.

5.Assertion (A): A ray of light travelling from a rarer medium to a denser medium slows down and bends away from the normal. When it travels from a denser medium to a rarer medium, it speeds up and bends towards the normal.

Reason (R): The speed of light is higher in a rarer medium than a denser medium.

6.Assertion (A): The mirrors used in search lights are concave mirrors.

Reason (R): In concave mirror the image formed is always virtual.

7.Assertion (A): Light travels faster in glass than in air.

Reason (R): Glass is denser than air.

8.Assertion (A): Concave mirrors are used as make-up mirrors.

Reason (R): When the face is held within the focus of a concave mirror, then a diminished image of the face is seen in the concave mirror.

9.Assertion (A): Refractive index has no units.

Reason (R): The refractive index is a ratio of two similar quantities.

10.Assertion (A): The formula connecting u, v and f for a spherical mirror is valid only for mirrors whose sizes are very small compared to their radii of curvature.

Reason (R): Laws of reflection are strictly valid for plane surfaces but not for large spherical surfaces.

11.Assertion(A): A person cannot see his image in a concave mirror, unless, he is standing beyond the center of curvature of the mirror.

Reason (R) : In a concave mirror, image formed is real provided the object is situated beyond its focus.

12.Assertion(A): keeping a point object fixed, if a plane mirror is moved, the image will also moved.

Reason (R) : In case of a plane mirror, distance of object and its image is equal from any point on the mirror.

13.Assertion (A): If both plane mirror and object are moved through a distance x, then the image moves through a distance 3x.

Reason (R): When the object is fixed and plane mirror is moved through a distance x. Then the image is also move through the distance x.

14.Assertion(A): The focal length of the convex mirror will increase , if the mirror is placed in water.

Reason (R) : The focal length of the convex mirror of radius R is equal to, f=R/2.

15.Assertion(A): An object is placed at a distance of u from a convex mirror of focal length f and its image will form at infinity.

Reason (R) : The distance of image in convex mirror can never be infinity.

16.Assertion(A): Refractive index of glass with respect to air is different for red light and violet light.

Reason (R) : Refractive index of a pair of media depends on the wavelength of the light used.

17.Assertion(A): Light travels in a straight line.

Reason (R) : Transparent objects allow all the light to pass through them.

18.Assertion(A): Incident light is reflected in one direction from a smooth surface.

Reason (R) : Since the angle of incidence and the angle of reflection are same, a beam of parallel rays of light falling on a smooth surface is reflected as a beam of parallel light rays in one direction only.

19.Assertion(A): For observing traffic at back, the mirror for driver is convex.

Reason (R) : A convex mirror has a larger field of view than a plane mirror.

20.Assertion (A): A virtual image can be photographed.

Reason (R) : Only real images can be photographed.

Answer Key:

Q. No.

Answer

Q. No.

Answer

1

a

11

b

2

c

12

d

3

a

13

d

4

a

14

d

5

d

15

d

6

c

16

a

7

d

17

b

8

c

18

a

9

a

19

a

10

c

20

c

Chapter 11 – Human Eye And The Colourful World

In the following questions, a statement of assertion (A) is followed by a statement of reason (R). Mark the correct choice as:

(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.

(b) If both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.

(c) If Assertion is true, but Reason is false.

(d) If Assertion is false, but Reason is true.

(e) If Assertion and Reason both are false.

1.Assertion(A) : White light is dispersed into its seven-colour components by a prism.

Reason (R) : Different colours of light bend through different angles with respect to the incident ray as they pass through a prism.

2.Assertion (A): The phenomenon of scattering of light by the colloidal particles gives rise to Tyndall effect.

Reason (R): The colour of the scattered light depends on the size of the scattering particles.

3.Assertion(A): When white light is passed through glass prism it splits into seven colours and this phenomenon is called dispersion.

Reason (R) : Different wavelengths travel with different speeds inside the prism.

4.Assertion(A) : A rainbow is sometimes seen in the sky in rainy season only when observer’s back is towards the Sun.

Reason (R) : Internal reflection in the water droplets cause dispersion and the final rays are in backward direction.

5.Assertion(A) : Danger signals are made of red colour.

Reason (R) : Velocity of red light in air is maximum, so signals are visible even in dark.

6.Assertion(A): The sky looks dark and black instead of blue in outer space.

Reason (R) : No atmosphere containing air in the outer space to scatter sunlight.

7.Assertion (A): The stars twinkle, while the planets do not.

Reason (R) : The stars are much bigger in size than the planets.

8.Assertion(A): The Sun appears flattened at sunrise and sunset.

Reason (R) : The apparent flattering of the Sun’s disc at sunrise and sunset is due to atmospheric refraction.

9.Assertion (A) : Blue colour of sky appears due to scattering of blue colour.

Reason (R) : Blue light has shortest wavelength.

10.Assertion(A) : Tyndall Effect is an optical phenomenon of light used to explain atmospheric refraction.

Reason (R) : The tiny particles of dust disperse sunlight in it falls through foliage in forest

11.Assertion(A) : On a clear summer night twinkling of stars is observed.

Reason (R) : The twinkling of stars is caused by dispersion of star light by the atmosphere.

12.Assertion(A) : On mid-day, the colour of the sunlight becomes white.

Reason (R) : No atmospheric refraction is caused due to overhead sun.

13.Assertion(A) : The light of violet colour deviates the most and the light of red colour the least, while passing through a prism.

Reason (R) : For a prism material, refractive index is highest for red light and lowest for the violet light. 119

14.Assertion(A) : Secondary rainbow is fainter than primary rainbow.

Reason (R) : Secondary rainbow formation is three step process and hence, the intensity of light is reduced at the second reflection inside the rain drop.

15.Assertion(A) : There exists two angles of incidence for the same magnitude of deviation (except minimum deviation) by a prism kept in air.

Reason (R) : In a prism kept in air, a ray is incident on first surface and emerges out of second surface. Now if another ray is incident on second surface (of prism)

16.Assertion(A) : A white light on passing through prism splits into its component colors as such that the red light emerges nearest to the base of the prism.

Reason (R) : Wavelength of red light is more than other component colours and hence, red light deviates least.

17.Assertion(A) : A rainbow is sometimes seen in the sky in rainy season only when observer’s back is towards the sun.

Reason (R) : Internal reflection in the water droplets cause dispersion and the final rays are in backward direction.

18.Assertion(A) : Rainbow is an example of the dispersion of sunlight by the water droplets.

Reason (R) : Light of shorter wavelength is scattered much more than light of larger wavelength.

19.Assertion(A) : The twinkling of stars is due to the fact that refractive index of the earth’s atmosphere fluctuates.

Reason (R) : In cold countries, the phenomenon of looming (i.e., ship appears in the sky) takes place, because refractive index of air decreases with height.

20.Assertion(A) : Danger signals are made of red colour.

Reason (R) : Velocity of red light in air is maximum, so signals are visible even in dark.

Answer Key:

Q. No.

Answer

Q. No.

Answer

1

a

11

d

2

b

12

a

3

a

13

C

4

a

14

a

5

c

15

a

6

a

16

a

7

b

17

a

8

a

18

c

9

a

19

b

10

c

20

c

Also Read:

(This Article has not been edited by NEWSUP18 and it is auto-generated from a syndicated feed.)

(Like our Facebook page for the latest posts, as well as follow us on Google News and Twitter. )

Share This