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      Class 9 Science

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      • Class 09
      • Class 9 Science
      CoursesClass 09ScienceClass 9 Science
      • 01.Matter in Our Surroundings
        9
        • Lecture1.1
          Matter and Its Properties 39 min
        • Lecture1.2
          States of Matter and Compressibility & Rigidity 21 min
        • Lecture1.3
          Moving through, Fluidity, Density, Diffusion, Pressure 26 min
        • Lecture1.4
          Change of State of Matter 56 min
        • Lecture1.5
          Evaporation and Boiling 39 min
        • Lecture1.6
          Cooling Effect of Evaporation Two More States of Matter 22 min
        • Lecture1.7
          Chapter Notes – Matter in Our Surroundings
        • Lecture1.8
          NCERT Solutions – Matter in Our Surroundings
        • Lecture1.9
          Revision Notes Matter in Our Surroundings
      • 02.Is Matter Around Us Pure
        9
        • Lecture2.1
          Elements and Compounds 20 min
        • Lecture2.2
          Mixtures, Homogeneous & Heterogeneous and Chemical & Physical Change 37 min
        • Lecture2.3
          Solution, Suspension, Colloid and Tyndal Effect 48 min
        • Lecture2.4
          Terms related to Solution and Solubility 42 min
        • Lecture2.5
          Separation of Mixtures 47 min
        • Lecture2.6
          Cleaning Drinking Water and Classification of Matter 29 min
        • Lecture2.7
          Chapter Notes – Is Matter Around Us Pure
        • Lecture2.8
          NCERT Solutions – Is Matter Around Us Pure
        • Lecture2.9
          Revision Notes Is Matter Around Us Pure
      • 03.Atoms and Molecules
        7
        • Lecture3.1
          Atom and its Properties, Atomic Mass, Molecule and Molecular Mass 40 min
        • Lecture3.2
          Ions, Valency and Writing the formulae of Compounds 47 min
        • Lecture3.3
          Mole Concept 42 min
        • Lecture3.4
          Calculation of no. of Moles, Percentage of an Element in a Compound and Laws of Chemical Combination 30 min
        • Lecture3.5
          Chapter Notes – Atoms and Molecules
        • Lecture3.6
          NCERT Solutions – Atoms and Molecules
        • Lecture3.7
          Revision Notes Atoms and Molecules
      • 04.Structure of The Atom
        7
        • Lecture4.1
          Charged Particles in Matter and Discovery of Sub – atomic Particles 31 min
        • Lecture4.2
          Atomic Model by J.J Thomson’s Model and Rutherford 57 min
        • Lecture4.3
          Ion, Mass Number, Isotopes, Isobar and Fractional Mass number of Elements 01 hour
        • Lecture4.4
          Electron Distribution in Orbits and Valency 01 hour
        • Lecture4.5
          Chapter Notes – Structure of The Atom
        • Lecture4.6
          NCERT Solutions – Structure of The Atom
        • Lecture4.7
          Revision Notes Structure of The Atom
      • 05.Cell - Fundamental Unit of Life
        7
        • Lecture5.1
          Introduction to Cell and Its Structure – Cell Wall 31 min
        • Lecture5.2
          Cell Membrane, Cytoplasm, Nucleus 32 min
        • Lecture5.3
          Ribosomes, Endoplasmic Reticulum, Golgi bodies, Lisosomes, Mitocondria 38 min
        • Lecture5.4
          Plastids, Vacuole; Types of Cell and Transport through Plasma Membrane 33 min
        • Lecture5.5
          Chapter Notes – Cell – Fundamental Unit of Life
        • Lecture5.6
          NCERT Solutions – Cell – Fundamental Unit of Life
        • Lecture5.7
          Revision Notes Cell – Fundamental Unit of Life
      • 06.Tissues
        8
        • Lecture6.1
          Division of Labour, Plant Tissues – Merismatic Tissue 20 min
        • Lecture6.2
          Plant Tissue-Permanent Tissue: Simple Permanent Tissue 34 min
        • Lecture6.3
          Plant Tissue-Permanent Tissue: Complex and Protective Tissue 31 min
        • Lecture6.4
          Animal Tissue- Muscular Tissue and Nervous Tissue 27 min
        • Lecture6.5
          Animal Tissue- Connective Tissue and Epithelial Tissue 42 min
        • Lecture6.6
          Chapter Notes – Tissues
        • Lecture6.7
          NCERT Solutions – Tissues
        • Lecture6.8
          Revision Notes Tissues
      • 07.Diversity in Living Organisms
        8
        • Lecture7.1
          Introduction to Biodiversity and Classification, Nomenclature 35 min
        • Lecture7.2
          The Five Kingdoms 29 min
        • Lecture7.3
          Plantae Kingdom 42 min
        • Lecture7.4
          Animalia Kingdom 01 hour
        • Lecture7.5
          Classification of Chordates and Revision of Animalia Kingdom 33 min
        • Lecture7.6
          Chapter Notes – Diversity in Living Organisms
        • Lecture7.7
          NCERT Solutions – Diversity in Living Organisms
        • Lecture7.8
          Revision Notes Diversity in Living Organisms
      • 08.Motion
        11
        • Lecture8.1
          Straight Line Motion, Position, Vector and Scalar; 23 min
        • Lecture8.2
          Distance & Displacement 48 min
        • Lecture8.3
          Speed and Velocity 57 min
        • Lecture8.4
          Acceleration and Deacceleration, Uniform & Non-uniform Acceleration 47 min
        • Lecture8.5
          Equations of Uniformly Accelerated Motion 58 min
        • Lecture8.6
          Uniform Circular Motion 30 min
        • Lecture8.7
          Graphical representation of Motion 30 min
        • Lecture8.8
          Calculations Using Graph 28 min
        • Lecture8.9
          Chapter Notes – Motion
        • Lecture8.10
          NCERT Solutions – Motion
        • Lecture8.11
          Revision Notes Motion
      • 09.Force and Newtons Laws of Motion
        12
        • Lecture9.1
          Force and Net or Resultant Force 46 min
        • Lecture9.2
          Newton’s 1st Law 46 min
        • Lecture9.3
          Momentum 46 min
        • Lecture9.4
          Newton’s 2nd Law 27 min
        • Lecture9.5
          Newton’s 2nd Law in Terms of Acceleration; 42 min
        • Lecture9.6
          Newton’s 1st Law from 2nd law and Practical Examples of Newton’s 2nd Law 42 min
        • Lecture9.7
          Newton’s 3rd Law and its Practical Examples 35 min
        • Lecture9.8
          Conservation of Momentum 33 min
        • Lecture9.9
          Practical Applications of Conservation of Momentum 29 min
        • Lecture9.10
          Chapter Notes – Force and Newtons Laws of Motion
        • Lecture9.11
          NCERT Solutions – Force and Newtons Laws of Motion
        • Lecture9.12
          Revision Notes Force and Newtons Laws of Motion
      • 10.Gravitation
        9
        • Lecture10.1
          Universal Law of Gravitation and Free Fall 41 min
        • Lecture10.2
          Falling Bodies: case 1 46 min
        • Lecture10.3
          Falling bodies: case 2 and Air Resistance 42 min
        • Lecture10.4
          Value of g, Mass and Weight, Weight on Moon, Circular Motion and Gravitation 48 min
        • Lecture10.5
          Thrust and Pressure and Pressure in fluids 37 min
        • Lecture10.6
          Archimedes Principle; Density 37 min
        • Lecture10.7
          Chapter Notes – Gravitation
        • Lecture10.8
          NCERT Solutions – Gravitation
        • Lecture10.9
          Revision Notes Gravitation
      • 11.Work and Energy
        7
        • Lecture11.1
          Work and Workdone Against Gravity, Oblique Displacement 01 hour
        • Lecture11.2
          Energy and Different Forms of Energy, Derivation of Formulae of K.E. 58 min
        • Lecture11.3
          Transformation of Energy and Law of Conservation of Energy 01 hour
        • Lecture11.4
          Rate of doing Work and Commercial Unit of Energy 43 min
        • Lecture11.5
          Chapter Notes – Work and Energy
        • Lecture11.6
          NCERT Solutions – Work and Energy
        • Lecture11.7
          Revision Notes Work and Energy
      • 12.Sound
        8
        • Lecture12.1
          Production and Propagation of Sound and Medium for Sound 30 min
        • Lecture12.2
          Frequency and Velocity of Sound Wave, Characteristic of Sound 01 hour
        • Lecture12.3
          Sonic Boom, Light faster than Sound, Reflection of Sound, Echo and Reverberation 56 min
        • Lecture12.4
          Types of Sound Based on Frequency 42 min
        • Lecture12.5
          Human Ear and Intensity of Sound 25 min
        • Lecture12.6
          Chapter Notes – Sound
        • Lecture12.7
          NCERT Solutions – Sound
        • Lecture12.8
          Revision Notes Sound
      • 13.Why do We Fall Ill
        7
        • Lecture13.1
          Factors Determining Health, Disease, Look of Disease, Cause of Disease, Types of Diseases 24 min
        • Lecture13.2
          Infectious Diseases, Immune System, Treatment of Diseases 55 min
        • Lecture13.3
          Prevention from Disease, Vaccination – Immunisation 36 min
        • Lecture13.4
          AIDS, Different Modes for Different Diseases 18 min
        • Lecture13.5
          Chapter Notes – Why do We Fall Ill
        • Lecture13.6
          NCERT Solutions – Why do We Fall Ill
        • Lecture13.7
          Revision Notes Why do We Fall Ill
      • 14.Natural Resources
        7
        • Lecture14.1
          Natural Resource-Air and its Pollution 57 min
        • Lecture14.2
          Natural Resource-Water and Soil and its Pollution 49 min
        • Lecture14.3
          Biogeochemical Cycles 33 min
        • Lecture14.4
          Green House Effect, Global Warming and Ozone Layer Depletion 30 min
        • Lecture14.5
          Chapter Notes – Natural Resources
        • Lecture14.6
          NCERT Solutions – Natural Resources
        • Lecture14.7
          Revision Notes Natural Resources
      • 15.Improvements in Food Resources
        7
        • Lecture15.1
          Various Revolution Held in India; Types of Crops; Crop Season; Crop Variety Improvement 31 min
        • Lecture15.2
          Crop Production Improvement 45 min
        • Lecture15.3
          Crop Protection Improvement and Organic Farming 29 min
        • Lecture15.4
          Animal Husbandry 40 min
        • Lecture15.5
          Chapter Notes – Improvements in Food Resources
        • Lecture15.6
          NCERT Solutions – Improvements in Food Resources
        • Lecture15.7
          Revision Notes Improvements in Food Resources

        NCERT Solutions – Structure of The Atom

        Intext Questions

        Q.1     What are canal rays?
        Sol.      Canal rays are positively charged radiations. These rays consist of positively charged particles known as protons. They were discovered by Gold stein in 1886.


        Q.2     If an atom contains one electron and one proton, will it carry any charge or not?
        Sol.      An electron is a negatively charged particle, whereas a proton is a positively charged particle. The magnitude of their charges is equal. Therefore, an atom containing one electron and one proton will not carry any charge. Thus, it will be a neutral atom.


        Page 49

        Q.1    On the basis of Thomson’s model of an atom, explain how the atom is neutral as a whole.
        Sol.    According to Thomson’s model of the atom, an atom consists of both negatively and positively charged particles. The negatively charged particles are embedded in the positively charged sphere. These
        negative and positive charges are equal in magnitude. Thus, by counterbalancing each other’s effect, they make an atom neutral.


        Q.2     On the basis of Rutherford’s model of an atom, which subatomic particle is present in the nucleus of an atom?
        Sol.      On the basis of Rutherford’s model of an atom, protons (positively-charged particles) are present in the nucleus of an atom.


        Q.3     Draw a sketch of Bohr’s model of an atom with three shells.
        Sol.
        4


        Q.4    What do you think would be the observation if the α-particle scattering experiment is carried out using a foil of a metal other than gold?
        Sol.     If the α-scattering experiment is carried out using a foil of a metal rather than gold, there would be no change in the observation. In the α-scattering experiment, a gold foil was taken because gold is malleable and a thin foil of gold can be easily made. It is difficult to make such foils from other metals.


        Page 49

        Q.1     Name the three sub-atomic particles of an atom.
        Sol.     The three sub-atomic particles of an atom are:
                   (i) Protons
                   (ii) Electrons, and
                   (iii) Neutrons


        Q.2     Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?
        Sol.      Helium atom has two neutrons. The mass of an atom is the sum of the masses of protons and neutrons present in its nucleus. Since helium atom has two protons, mass contributed by the two protons is (2 × 1) u = 2 u. Then, the remaining mass (4 − 2) u = 2 u is contributed by 2u /1u = 2 neutrons.


        Page 50

        Q.1     Write the distribution of electrons in carbon and sodium atoms?
        Sol.     The total number of electrons in a carbon atom is 6. The distribution of electrons in carbon atom is given by: First orbit or K-shell = 2 electrons
        Second orbit or L-shell = 4 electrons
        Or, we can write the distribution of electrons in a carbon atom as 2, 4.
        The total number of electrons in a sodium atom is 11. The distribution of electrons in sodium atom is given by:
        First orbit or K-shell = 2 electrons
        Second orbit or L-shell = 8 electrons
        Third orbit or M-shell = 1 electron
        Or, we can write distribution of electrons in a sodium atom as 2, 8, 1.


        Q.2     If K and L shells of an atom are full, then what would be the total number of electrons in the atom?
        Sol.      The maximum number of electrons that can occupy K and L-shells of an atom are 2 and 8 respectively. Therefore, if K and L-shells of an atom are full, then the total number of electrons in the atom would be (2 + 8) = 10 electrons.


        Page 52

        Q.1     How will you find the valency of chlorine, sulphur and magnesium?
        Sol.      If the number of electrons in the outermost shell of the atom of an element is less than or equal to 4, then the valency of the element is equal to the number of electrons in the outermost shell . On the other hand, if the number of electrons in the outermost shell of the atom of an element is greater than 4, then the valency of that element is determined by subtracting the number of electrons in the outermost shell from 8. The distribution of electrons in chlorine, sulphur, and magnesium atoms are 2, 8, 7; 2, 8, 6 and 2, 8, 2 respectively. Therefore, the number of electrons in the outer most shell of chlorine, sulphur, and magnesium atoms are 7, 6, and 2 respectively. Thus, the valency of chlorine = 8 −7 = 1 The valency of sulphur = 8 − 6 = 2 The valency of magnesium = 2


        Q.1     If number of electrons in an atom is 8 and number of protons is also 8, then (i) what is the atomic number  of the atom and (ii) what is the charge on the atom?
        Sol.      (i) The atomic number is equal to the number of protons. Therefore, the atomic number of the atom is 8.
        (ii) Since the number of both electrons and protons is equal, therefore, the charge on the atom is 0.


        Q.2     With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.
        Sol.     Mass number of oxygen = Number of protons + Number of neutrons = 8 + 8 = 16
        Mass number of sulphur = Number of protons + Number of neutrons
        = 16 +16
        = 32


        Page 53 

        Q.1     For the symbol H, D and T  tabulate three sub – atomic particles found each of them.
        Sol.    

        Symbol Proton Neutron Electron
        H 1 0 1
        D 1 1 1

         


        Q.2     Write the electronic configuration of any pair of isotopes and isobars.
        Sol.     Two isotopes of carbon are  126Cand146C
                   The electronic configuration  of 126C is 2, 4.
                   The electronic configuration  of 146C  is 2, 4.
        [Isotopes have same electronic configuration ]
        4029Caand4018Ar are a pair of  isobars
        The electronic configuration  of 4029Ca 2, 8, 8, 2
        The electronic configuration  of 4018Ar 2, 8, 8.

        Exercise

        Q.1     Compare the properties of electrons, protons and neutrons.
        Sol.

        Electron  Proton Neutron 
        (i) Electron are present outside
        the nucleus of an atom.
        (i) Proton are present in
        the nucleus of an atom.
        (i) Neutron are present in the
        nucleus of an atom.
        (ii) Electron are negatively
        charged
        (ii) Proton are positively
        charged.
        (ii) Neutron are neutral.
        (iii) The mass of an electron is
        considered to negligible.
        (iii) The mass of a proton is
        approximately 2000 times as the
        mass of an electron
        (iii) The mass of neutron is nearly
        equal to the mass  of a proton.

         


        Q.2     What are the limitations of J.J. Thomson’s model of the atom?
        Sol.      According to J.J. Thomson’s model of an atom, an atom consists of a positively charged sphere with electrons embedded in it. However, it was later found that the positively charged particles reside at the center of the atom called the nucleus, and the electrons revolve around the nucleus.


        Q.3    What are the limitations of Rutherford’s model of the atom?
        Sol.     According to Rutherford’s model of an atom, electrons revolve around the nucleus in fixed orbits. But, an electron revolving in circular orbits will not be stable because during revolution, it will experience
        acceleration. Due to acceleration, the electrons will lose energy in the form of radiation and fall into the
        nucleus. In such a case, the atom would be highly unstable and collapse.


        Q.4     Describe Bohr’s model of the atom.
        Sol.     Bohr’s model of the atom Niels Bohr proposed the following postulates regarding the model of the atom.
                   (i) Only certain orbits known as discrete orbits of electrons are allowed inside the atom.
                   (ii) While revolving in these discrete orbits, the electrons do not radiate energy.These discrete orbits or
        shells are shown in the following diagram.

        3

        The first orbit (i.e., for n = 1) is represented by letter K. Similarly, for n = 2, it is L − shell, for n = 3, it is M − shell and for n = 4, it is N − shell. These orbits or shells are also called energy levels.


        Q.5     Compare all the proposed models of an atom given in this chapter
         Sol.

        Thomson’s
        model
        Rutherford’s model Bohr’s model
        An atom consists of a
        positively charged sphere
        with electrons embedded in it.
        An atom consists of a positively
        charged particles concentrated
        at the center known as the nucleus.
        The size of the nucleus is very small
        as compared to the size of the atom.
        The electron revolve around the
        nucleus in well – defined orbits.
        There are only certain
        orbits know as discrete
        orbits inside the atom in
        which electrons revolve around
        the nucleus. Electrons do not
        radiate energy while revolving.

         


        Q.6     summarize the rules for writing of distribution of electrons in various shells for the first eighteen elements.
        Sol.     The rules for writing of the distribution of electrons in various shells for the first eighteen elements are given below.
        (i) The maximum number of electrons that a shell can accommodate is given by the formula  ‘2n2‘, where ‘n’ is the orbit number or energy level index (n = 1, 2, 3…).
        The maximum number of electrons present in an orbit  of n = 1 given by
        2n2=2×12=2
        Similarly, for second orbit, it is  2n2=2×22=8
        For third orbit, it is 2n2=2×32=18
        And so on …..
        (ii) The outermost orbit can be accommodated by a maximum number of  8 electrons.
        (iii) Shells are filled with electrons in a step wise manner i.e., the outer shell is not  occupied with electrons unless the inner shells are completely filled with electrons.


        Q.7     Define valency by taking examples of silicon and oxygen.
        Sol.      The valency of an element is the combining capacity of that element. The valency of an element is determined by the number of valence electrons present in the atom of that element. If the number of
        valence electrons of the atom of an element is less than or equal to four, then the valency of that element
        is equal to the number of valence electrons. For example, the atom of silicon has four valence electrons.
        Thus, the valency of silicon is four. On the other hand, if the number of valence electrons of the atom of an element is greater than four, then the valency of that element is obtained by subtracting the number of valence electrons from eight. For example, the atom of oxygen has six valence electrons. Thus, the valency of oxygen is (8 − 6) i.e., two.


        Q.8     Explain with examples (i) Atomic number, (ii) Mass number, (iii) Isotopes and (iv) Isobars. Give any two uses of isotopes.
        Sol.      (i) Atomic number
        The atomic number of an element is the total number of protons present in the atom of that element. For example, nitrogen has 7 protons in its atom. Thus, the atomic number of nitrogen is 7.
                   (ii) Mass number
        The mass number of an element is the sum of the number of protons and neutrons present in the atom of that element. For example, the atom of boron has 5 protons and 6 neutrons. So, the mass number of boron is 5 + 6 = 11.
                   (iii) Isotopes And, the percentage of isotope is (100 − 10) % = 90%.


        Q.12     If Z = 3, what would be the valency of the element? Also, name the element.
        Sol.        By Z = 3, we mean that the atomic number of the element is 3. Its electronic configuration is 2, 1. Hence, the valency of the element is 1 (since the outermost shell has only one electron).
        Therefore, the element with Z = 3 is lithium.


        Q.13     Composition of the nuclei of two atomic species X and Y are given as under X Y
        Protons = 6 6
        Neutrons = 6 8
        Give the mass numbers of X and Y. What is the relation between the two species?
        Sol.        Mass number of X = Number of protons + Number of neutrons
        = 6 + 6
        = 12
        Mass number of Y = Number of protons + Number of neutrons
        = 6 + 8
        = 14
        These two atomic species X and Y have the same atomic number, but different mass numbers. Hence, they are isotopes.


        Q.14     For the following statements, write T for ‘True’ and F for ‘False’.
                     (a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons.
                     (b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.
                     (c) The mass of an electron is about 1/2000 times that of proton.
                     (d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.
        Sol.       (a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons. (F)
        (b) A neutron is formed by an electron and a proton combining together. Therefore, itis neutral. (F)
        (c) The mass of an electron is about 1/2000 times that of proton. (T)
        (d) An isotope of iodine is used for making tincture iodine, which is used as a medicine. (T)


        Q.15     Put tick ( – ) against correct choice and cross ( x ) against wrong choice in the following question: Rutherford’s alpha-particle scattering experiment was responsible for the discovery of
                     (a) Atomic nucleus
                     (b) Electron
                     (c) Proton
                     (d) Neutron
        Sol.       Rutherford’s alpha-particle scattering experiment was responsible for the discovery of
        (a) Atomic nucleus ( – )
        (b) Electron ( x )
        (c) Proton ( x )
        (d) Neutron ( x )


        Q.16     Put tick ( – ) against correct choice and cross ( x ) against wrong choice in the following
        question: Isotopes of an element have
                     (a) the same physical properties
                     (b) different chemical properties
                     (c) different number of neutrons
                     (d) different atomic numbers
        Sol.       Isotopes of an element have
        (a) the same physical properties ( x )
        (b) different chemical properties ( x )
        (c) different number of neutrons ( – )
        (d) different atomic numbers ( x )


        Q.17     Put tick ( – ) against correct choice and cross ( x ) against wrong choice in the
        following question:
        Number of valence electrons in Cl− ion are:
                     (a) 16
                     (b) 8
                     (c) 17
                     (d) 18
        Sol.       Number of valence electrons in Cl− ion are:
        (a) 16 ( x )
        (b) 8 ( – )
        (c) 17 ( x )
        (d) 18 ( x )


        Q.18     Which one of the following is a correct electronic configuration of sodium?
                      (a) 2, 8
                      (b) 8, 2, 1
                      (c) 2, 1, 8
                      (d) 2, 8, 1
        Sol.        (d) The correct electronic configuration of sodium is 2, 8, 1.
        This page is about: structure of atom class 9 ncert solutions, structure of atom class 9 notes, ncert solutions for class 9 science chemistry chapter 4, ncert solutions for class 9 science chapter 4, structure of atomclass 9 solutions, structure of the atom class 9, Structure of atom class 9, ncert solution for class 9 science chapter 4, if an atom contains one electron and one proton will it carry any charge or not, On the basis of Thomsons model of an atom explain how the atom is neutral as a whole

         

        Exemplar

        Multiple Choice Questions 

        Q.1 Which of the following correctly represent the electronic distribution in the Mg atom?

        (a) 3, 8, 1

        (b) 2, 8, 2

        (c) 1, 8, 3

        (d) 8, 2, 2

        Sol. (b)


        Q.2 Rutherford’s ‘alpha (α) particles scattering experiment’ resulted in to discovery of

        (a) Electron

        (b) Proton

        (c) Nucleus in the atom

        (d) Atomic mass

        Sol. (c)


        Q.3 The number of electrons in an element x is 15 and the number of neutrons is 16. Which of the following is the correct representation of the element?

        (a) 31 15 x

        (b) 31 16 x

        (c) 16 15 x

        (d) 15 16 x

        Sol. (a)


        Q.4 Dalton’s atomic theory successfully explained

        (i) Law of conservation of mass

        (ii) Law of constant composition

        (iii) Law of radioactivity

        (iv) Law of multiple proportion

        (a) (i), (ii) and (iii)

        (b) (i), (iii) and (iv)

        (c) (ii), (iii) and (iv)

        (d) (i), (ii) and (iv)

        Sol. (d)


        Q.5 Which of the following statements about Rutherford’s model of atom are correct?

        (i) Considered the nucleus as positively charged

        (ii) Established that the α–particles are four times as heavy as a hydrogen atom

        (iii) Can be compared to solar system

        (iv) Was in agreement with Thomson’s model

        (a) (i) and (iii)

        (b) (ii) and (iii)

        (c) (i) and (iv)

        (d) Only (i)

        Sol. (a)


        Q.6 Which of the following are true for an element?

        (i) Atomic number = number of protons + number of electrons

        (ii) Mass number = number of protons + number of neutrons

        (iii) Atomic mass = number of protons = number of neutrons

        (iv) Atomic number = number of protons = number of electrons

        (a) (i) and (ii)

        (b) (i) and (iii)

        (c) (ii) and (iii)

        (d) (ii) and (iv)

        Sol. (d)


        Q.7 In the Thomson’s model of atom, which of the following statements are correct?

        (i) The mass of the atom is assumed to be uniformaly distributed over the atom

        (ii) The positive charge is assumed to be uniformaly distributed over the atom

        (iii) The electrons are uniformaly distributed in the positively charged sphere

        (iv) The electrons attract each other to stabilise the atom

        (a) (i), (ii) and (iii)

        (b) (i) and (iii)

        (c) (i) and (iv)

        (d) (i), (iii) and (iv)

        Sol. (a)


        Q.8 Rutherford’s α–particle scattering experiment showed that

        (i) Electrons have negative charge

        (ii) The mass and positive charge of the atom is concentrated in the nucleus

        (iii) Neutron exists in the nucleus

        (iv) Most of the space in atom is empty

        Which of the above statements are correct?

        (a) (i) and (iii)

        (b) (ii) and (iv)

        (c) (i) and (iv)

        (d) (iii) and (iv)

        Sol. (b)


        Q.9 The ion of an element has 3 positive charges. Mass number of the atom is 27 and the number of neutrons is 14. What is the number of electrons in the ion?

        (a) 13

        (b) 10

        (c) 14

        (d) 16

        Sol. (b)


        Q.10 Identify the Mg2+ ion from the Fig.where, n and p represent the number of neutrons and protons respectively

        Sol.(d)


        Q.11 In a sample of ethyl ethanoate (CH3COOC2H5) the two oxygen atoms have the same number of electrons but different number of neutrons. Which of the following is the correct reason for it?

        (a) One of the oxygen atoms has gained electrons

        (b) One of the oxygen atoms has gained two neutrons

        (c) The two oxygen atoms are isotopes

        (d) The two oxygen atoms are isobars.

        Sol. (c)


        Q.12 Elements with valency 1 are

        (a) Always metals

        (b) Always metalloids

        (c) Either metals or non-metals

        (d) Always non-metals

        Sol. (c)


        Q.13 The first model of an atom was given by

        (a) N. Bohr

        (b) E. Goldstein

        (c) Rutherford

        (d) J.J. Thomson

        Sol. (d)


        Q.14 An atom with 3 protons and 4 neutrons will have a valency of

        (a) 3

        (b) 7

        (c) 1

        (d) 4

        Sol. (c)


        Q.15 The electron distribution in an aluminium atom is

        (a) 2, 8, 3

        (b) 2, 8, 2

        (c) 8, 2, 3

        (d) 2, 3, 8

        Sol. (a)


        Q.16 Which of the following in Fig. do not represent Bohr’s model of an atom correctly?

        (a) (i) and (ii)

        (b) (ii) and (iii)

        (c) (ii) and (iv)

        (d) (i) and (iv)

        Sol. (c)


        Q.17 Which of the following statement is always correct?

        (a) An atom has equal number of electrons and protons.

        (b) An atom has equal number of electrons and neutrons.

        (c) An atom has equal number of protons and neutrons.

        (d) An atom has equal number of electrons, protons and neutrons

        Sol. (a)


        Q.18 Atomic models have been improved over the years. Arrange the following atomic models in the order of their chronological order

        (i) Rutherford’s atomic model

        (ii) Thomson’s atomic model

        (iii) Bohr’s atomic model

        (a) (i), (ii) and (iii)

        (b) (ii), (iii) and (i)

        (c) (ii), (i) and (iii)

        (d) (iii), (ii) and (i)

        Sol. (c)

        Prev Chapter Notes – Structure of The Atom
        Next Revision Notes Structure of The Atom

          1 Comment

        1. Ayush maurya
          July 20, 2022
          Reply

          Class 9th chemistry notes structure of atom send me

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