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CBSE Class 9 Science Exam 2018: Important Short Answer Type Questions

Jan 23, 2018 17:43 IST
    Important Short Answer Type Questions
    Important Short Answer Type Questions

    Here we are providing a set of important questions in the category of short answer type questions for CBSE class 9 Science annual exam 2018. These are the questions which will be asked for 3 marks in the ‘A-Section’ of science exam. There will be a total of 10 short answer type questions.

    All the questions given here are provided with detailed explanation which will make your preparation easy.

    Given below are some very important questions for short answer type questions category in class 9 Science exam:

    Question 1. (a) Draw a sketch of Bohr’s model of an atom with three shells.

    (b) If K and L shell of an atom are full, then what would be the total number of electrons in the atom?

    Answer.

    (a) Bohr’s model of an atom with three shells is presented in the following image:

    CBSE Class 9 Solution 1

    (b) K shell can accommodate maximum 2 electrons and L shell can accommodate 8 electrons. Thus, if both K and L shells are full then the total number of electrons must be 10.

    Question 2. What is role of tissues present in multi-cellular organisms? (3 Marks)

    Answer.

    The formation of tissues is important in multi-cellular organisms as :

    (a) Grouping of cells and performing a single function by the group shows division of labour.

    (b) Tissues combine to form organ, organ to organ system and organ systems to organisms.

    (c) Due to improved organisation and higher efficacy organisms have high survival rate.

    Question 3. Give reasons for the following :
    (a) Ice though being a solid floats on water.
    (b) A gas fills completely the vessel in which it is kept ?
    (c) Rate of evaporation of an aqueous solution decreases with increase in humidity

    Answer.

    (a) Density of ice is less than that of water. This is on account of the reason that the structure of ice is porous. Therefore, for a given mass , the volume of ice is more than that of water.

    (b) This happens because the particles of gas have the high kinetic energy due to which they keep moving and hence exert pressure on the walls of the vessel in which it is kept and hence they readily fill the vessel completely, attaining the same volume as that of the vessel.

    (c) Humidity is the amount of water vapour present in air. So, the increase in humidity means that air has high water content due to which it becomes difficult for air to take in more water molecues formed as a result of evaporation. Hence, the rate of evaporation of an aqueous solution decreases with the increase of humidity.

    Question 4. (a) Name two properties of a substance to check its purity?

    (b) Alloys cannot be separated by physical means, though it is considered mixture, Why?

    Answer.

    (a) A pure substance has a fixed melting point or boiling point at constant pressure. The purity of a substance can be tested by checking its melting point or boiling point. If a substance is impure i.e. it contains traces of another substance, the melting and boiling point of that substance will change.

    (b) Alloys are homogeneous mixtures of metals and cannot be separated into their components by physical methods. But still, an alloy is considered as a mixture because it shows the properties of its constituents and can have variable composition.

    Question 5. When we open the cap of a cola drink (or any carbonated beverage), why does excess of bubbles come out?

    Answer.

     A cola (or carbonated) beverage is produced by dissolving carbon dioxide in the drink 
    solution under pressure. Increase in pressure increases the solubility of gases. Therefore, more carbon dioxide dissolves at the higher pressure. When this pressure is suddenly released, e.g. by removing the cap of the bottle, carbon dioxide is less soluble, and it comes out in as bubbles from the solution.

    Question 6. Give reasons for the followng:
    (i) A liquid generally flows easily
    (ii) Ice at 0o appears colder to the mouth than water at 0°C. Why?
    (iii) Doctors advise to put strips of wet cloth on the forehead of a person having high temperature.

    Answer:

    (i) A liquid generally flows easily because the intermolecular space between the liquid particles are more as compared to solids. Moreover there particles are loosely packed due to the presence of a little force of attraction between them.
    (ii) Ice at 0o C appears colder to the mouth than water at 0 C because the ice absorbs more latent heat as compared to water at the same temperature.
    (iii) Doctors advise to put strips of wet cloths on the forehead of a person having high temperature because the water absorbs the heat of the body and then evaporates thereby reducing the temperature of body.

    Question 7. (a) Who discovered vaccine for the first time?

    (b) What is an antibiotic? Give two examples.

    Answer.

    (a) Edward Jenner discovered vaccine.

    (b) A substance or compound that kills or inhibits the growth of bacteria is called antibiotic.
    Examples : Penicillin, Ampicillin.

    Question 8. Why air is a mixture not a compound? Give reasons.

    Answer.

     Air is considered as a mixture for the following reasons:

    • Air does not have a fixed composition. Its composition varies from place to place.
    • The components of air can be separated by a physical method such as fractional distillation of liquid air.
    • Liquid air does not have a definite boiling point.
    • We can prepare air artificially by mixing the various components of air in the same proportions in which they occur at a place. This is a physical process because no energy changes occur.

    Question 9. Calculate the mass of glucose and mass of water required to make 200g of 25% solution of glucouse.

    Answer.

    Given mass of solution(M) = 200g
    Concentration of solution = 25%
    Since, Mass by Mass percentage of solution = mass of solute(m) × 100 / mass of solution(M).
    ⇒ 25 = m × 100/200g 
    ⇒ m = 25 × 200/100 = 50g
    ∴ Mass of solute = 50g
    mass of solvent (water) = M - m = 200g - 50g = 150g

    Question 10. How crystallization is better than evaporation?

    Answer.

    The process of evaporation gives residue which may contain impurities. When there is requirement to obtain solid without impurity, crystallization method is preferred.

    In general practice, impure solids are obtained by evaporation and are further purified by crystallization. e.g. salt obtained from sea is further purified by the process of crystallisation.

    Also in some other cases like in obtaining sugar crystals, simple evaporation cannot be used because sugar gets charred on heating to dryness. In such cases, crystallization method is applied.

    Question11. Give three examples of the range of variations that you see in life forms around you.

    Answer.

    The following range of variations can be seen in different life forms which occurs on Earth.

    (i) Variation in size: Some microscopic bacteria are few micrometre in size whereas blue whale
    and redwood trees of California are approximately of 30 metres and 100 metres respectively.

    (ii) Variation in lifespan : Some pine trees live for thousands of years while insects like mosquitoes die within a few days.

    (iii) Variation in body colours: Some life forms such as worms are colourless or even transparent whereas many of the birds, insects, flowers etc., are brightly coloured.

    Question12. When a bullet is fired from a rifle its momentum become 20 kg m/s. If the velocity of the bullet is 1000m/s what will be its mass?

    Answer.

    Given, Momentum (p) = 20 kg m/s

    Velocity (v) = 1000m/s

    Mass (m) =?

    We know that, Momentum (p) = Mass (m) x Velocity (v)

    Therefore, 20 kg m/s = m × 1000m/s

    ⟹          m=20 /1000

    ⟹          m= 0.02 kg =20 g

    Thus, mass of the bullet = 20 g

    Question13. Is it possible that an object is in the state of accelerated motion due to external force acting on it, but no work is being done by the force. Explain it with an example.

    Answer.

    Yes, it is possible, if an object is moving in a circular path because in that case the centripetal force always acts perpendicular to the direction of displacement.

    For example: Consider the motion of earth around sun. The earth is constantly moving in a direction perpendicular to the gravitation pull of sun, hence work done by the gravitational force is zero.

    Question14. What do you mean by active and passive immunisation ?

    Answer. 

    Active immunisation : It promotes the production of circulating antibodies against foreign antigens by injecting a small quantity of modified antigen into the bloodstream.
    Passive immunisation: It is the application of antibodies from an immune individual to non- immune patient. This treatment is used when an individual has been or probably will be, exposed to an infectious disease and there is insufficient time for active immunisation.

    Question15. (a) Explain the formation of acid rain.
    (b) What does the presence of smog in an area indicate?

    Answer. 

    Acid rain results when sulfur dioxide (SO2) and nitrogen oxides (NOX) present in atmosphere, react with water to form sulfuric and nitric acids. The Oxides of sulphur and nitrogen are produced by combustion of fossil fuels in industries, automobiles, thermal power plants and domestic appliances etc. Also the sulphur and nitrogen, present in fossil fuels form these oxides by reacting with oxygen of air by the process of combustion.

    (b) The presence of smog in an area indicates the high percentage of smoke released in the air by combustion of fossil fuel in industries, thermal power plants or automobiles. It is an indicator of air pollution.

    Question16. (a) What happens to the buoyant force as more and more volume of a solid object is immersed in a liquid? When does the buoyant force become maximum?

    (b)Define buoyant force. Name two factors on which buoyant force depends.

    Answer.

    (a) The buoyant or upthrust force increases as more and more volume of a solid object is immersed in a liquid. When object is fully immersed in water the buoyant force becomes maximum.

    (b)Fluid applies an upward force on a solid which is partially or fully submerged in liquid. This phenomenon is called buoyancy (Upthrust) and applied upward force is called buoyant force.

    Two factors on which buoyant force depends:

    • Volume or shape of object.

    • Density of fluid in which object is immersed.

    Question17. If the distance between two masses is increased by a factor of 5, by what factor would the mass of one of them have to be altered to maintain the same gravitational force?

    Answer.

    Let Gravitational constant = G

    Also, let M and  m be the masses of two objects and d be the distance between them

    Then gravitation force,

    CBSE Class 9 Solution 1(a)

    When the distance between two masses is increased by 5 times, then d’ = 5d

    So, new gravitation  force becomes,

    CBSE Class 9 Solution 1(b)

    Using equations (i) and (ii), we get:

    CBSE Class 9 Solution 1(c)

    Thus, to maintain  the same gravitational force, the mass should be increased by 25 times.

    All the CBSE class 9 short answer type questions provided here have been taken from the most important topics of class 9 Science. So, students may expect the similar questions in their class 9 Science annual exam 2018.

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