CBSE Class 9 Science Structure of The Atom Worksheet Set A

Question. Select the correct statements.
(i) An atom is divisible and consists of charged particles.
(ii) It was known by 1900 that the atom was not a simple, indivisible particle but contained at least one sub-atomic particle – the electron.
(iii) E. Goldstein in 1886 discovered the presence of new radiations called canal rays which led to the discovery of another sub-atomic particle – the proton.
(iv) Proton had a charge, equal in magnitude but opposite in sign to that of the electron and its mass was approximately 2000 times as that of the electron.
(v) The mass of an electron is considered to be negligible and its charge is minus one.
(a) (i), (ii) and (iii)
(b) (iii), (iv) and (v)
(c) (ii), (iii) and (iv)
(d) All the statements are correct.
Answer. D

Question. Rutherford concluded from the a-particle scattering experiment that
(i) most of the space inside the atom is empty because most of the α-particles passed through the gold foil without getting deflected.
(ii) very few particles were deflected from their path, indicating that the negative charge of the atom occupies very little space.
(iii) a very large fraction of α-particles were deflected by 180°°, indicating that all the negative charge and mass of the gold atom were not concentrated in a very small volume within the atom.
Identify the incorrect statements.
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (i), (ii) and (iii)
Answer. B

Question. Which of the following has the same number of electrons as an oxide ion (O^2–)?
(a) K⁺
(b) Mg²⁺
(c) Cl^–
(d) S^2–
Answer. B

Question. Select the correct statements.
(i) The radius of the nucleus is about 107 times less than the radius of the atom.
(ii) There is a positively charged centre in an atom called the nucleus. Nearly all the mass of an atom resides in the nucleus.
(iii) The electrons revolve around the nucleus in circular paths.
(iv) The size of the nucleus is very large as compared to the size of the atom.
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i), (ii) and (iii)
(d) All the statements are correct.
Answer. B

Question. Which pair of molecules has the same number of electrons?
(a) N₂ and F₂
(b) Cl₂ and CO₂
(c) H₂O and H₂S
(d) O₂ and C₂H₄
Answer. D

Question. 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)
Answer. C

Question. 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)
Answer. D

Question. The main drawback of Rutherford’s model of the atom is that
(a) it does not explain the stability of atom
(b) it does not show the location of protons
(c) it does not explain neutral nature of an atom
(d) it does not explain existence of a nucleus in an atom.
Answer. A

Question. The nucleon number of the bromine atom is 79 and its proton number is 35. Which of the following is true about the bromine atom?
(a) It has 79 neutrons.
(b) It has 44 electrons.
(c) Its electronic configuration contains three shells which has 7 electrons in outermost shell.
(d) It has similar chemical properties as chlorine.
Answer. D

Question. 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
Answer. B

Question. A monovalent anion has 10 electrons and 10 neutrons. The atomic number and mass number of the element are respectively ______ and _____.
(a) 10, 20
(b) 9, 18
(c) 11, 20
(d) 9, 19
Answer. D

Question. 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.
Answer. C

Question. An element L has 9 protons and its valency is 1. Another element M has valency 3 and 5.What is the difference in the number of electrons in L and M?
(a) 6
(b) 5
(c) 4
(d) 3
Answer. A

Question. An atom with 3 protons and 4 neutrons will have a valency of
(a) 3
(b) 7
(c) 1
(d) 4
Answer. C

Question. The electron distribution in an aluminium atom is
(a) 2, 8, 3
(b) 2, 8, 2
(c) 8, 2, 3
(d) 2, 3, 8
Answer. A

Question. In the Thomson’s model of atom, which of the following statements are correct?
(i) The mass of the atom is assumed to be uniformly distributed over the atom.
(ii) The positive charge is assumed to be uniformly distributed over the atom.
(iii) The electrons are uniformly 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)
Answer. A

Question. The relative atomic mass of naturally occurring chlorine is not a whole number. What is the reason for this?
(a) Chlorine atoms can have different numbers of neutrons.
(b) Naturally occurring chlorine cannot be obtained pure.
(c) Chlorine is unstable.
(d) The mass of the electrons has been included.
Answer. A

Question. Which one of the following is not isoelectronic with neon atom?
(a) 8O^2–
(b) 11Na⁺
(c) 9F^–
(d) 12Mg⁺
Answer. D

Question. The electronic configuration of elements
A, B, C and D are (2, 8, 1), (2, 8, 2), (2, 8, 6) and (2, 8, 7) respectively. Which of them can make an ion with two negative charges?
(a) A
(b) B
(c) C
(d) D
Answer. C

Question. Match the column I with column II and select the correct answer by choosing an appropriate option.
      Column I                           Column II
P. Mass of proton           1. 9.1 × 10^–28 g
Q. Charge of electron     2. 1.6 × 10^–19 C
R. Mass of electron        3. –1.6 × 10^–19 C
S. Charge on proton      4. 1.67 × 10^–27 kg
(a) P - 4, Q - 3, R - 1, S - 2
(b) P - 2, Q - 1, R - 4, S - 3
(c) P - 2, Q - 3, R - 4, S - 1
(d) P - 4, Q - 2, R - 1, S - 3
Answer. A

Question. Match the column I with column II and select the correct answer by choosing an appropriate option.
Column I                                   Column II
P. Neutron                               1. Rutherford’s atomic model
Q. Plum pudding model          2. Bohr’s atomic model
R. Mass of the atom is            3. Thomson’s atomic
concentrated at the                  model
centre of atom
S. Stationary orbit                  4. Chadwick
(a) P - 1, 4; Q - 1, 2, 3; R - 2; S - 1, 2, 3
(b) P - 1; Q - 1, 2, 3; R - 2; S - 1, 2
(c) P - 1; Q - 3; R - 2; S - 1
(d) P - 4; Q - 3; R - 1; S - 2
Answer. D

Question. Match the following:-
    List-I              List-II
(P) Proton         1. Thomson
(Q) Electron      2. Goldstein
(R) Neutron      3. Rutherford
(S) Nucleus      4. Chadwick
(a) P-4, Q-3, R-2, S-1
(b) P-1, Q-2, R-3, S-4
(c) P-2, Q-1, R-4, S-3
(d) P-2, Q-1, R-3, S-4
Answer. C

Question. Match the following:-
     List-I                             List-II
(P) Electrons                  1. Number of positively charged particles in nucleus
(Q) Carbon dating           2. Negatively charged particles
(R) Valence electrons      3. Technique to know age of fossils
(S) Atomic number         4. Number of electrons in outermost shell
(a) P-1, Q-2, R-3, S-4
(b) P-4, Q-3, R-2, S-1
(c) P-2, Q-4, R-3, S-1
(d) P-2, Q-3, R-4, S-1
Answer. D

Case I : Read the passage given below and answer the following questions.
The maximum number of the electrons which are permitted to be assigned to an energy shell of an atom is called the electron capacity of that shell. The distribution of electrons in different orbits or shell is governed by a scheme known as Bohr-Bury scheme.
According to this scheme :
(i) The maximum number of the electrons that can be present in any shell is given by the formula 2n2 where, n is the number of energy level.
(ii) The maximum number of electrons that can be accommodated in the outermost shell is 8.
Electrons are filled in the shells in a stepwise manner in increasing order of energy of the energy shell.

Question. What is the maximum electrons capacity of N shell?
(a) 24
(b) 8
(c) 18
(d) 32
Answer. D

Question. Identify the element with the configuration K-2, L-8, M-3.
(a) Aluminium
(b) Magnesium
(c) Sodium
(d) Beryllium
Answer. A

Question. Which of the following configuration represent sodium?
(a) 2, 8, 4
(b) 2, 8, 5
(c) 2, 3
(d) 2, 8, 1
Answer. D

Case II : Read the passage given below and answer the following questions.

The table shows the number of sub-atomic particles in arbitrary elements, A to H.
Atom   Number of protons  Number of electrons   Number of neutrons
A              1                           1                                  0
B              3                          3                                   4
C              4                          4                                   6
D              5                          5                                  5
E              6                          6                                  6
F              6                          6                                  7
G             9                          9                                 10
H             9                          9                                 11

Question. The pair of isotopes from the table is/are
(i) C and D
(ii) E and F
(iii) B and C
(iv) G and H
(a) (ii) only
(b) (iv) only
(c) (ii) and (iv) only
(d) (i), (ii), (iii) and (iv)
Answer. C

Question. Which of the given elements attains noble gas configuration by gaining an electron?
(i) A (ii) E
(iii) C (iv) H
(a) (iii) only
(b) (iv) only
(c) (i) and (iv) only
(d) (i) only
Answer. C

Question. Identify pair of isobars from the table.
(a) C and D
(b) B and E
(c) G and H
(d) E and F
Answer. A

Question. The atom _____ has nucleon number 13 and atom _____ has valency 3.
(a) G and F
(b) F and D
(c) C and E
(d) F and B
Answer. B

Case III : Look at the diagram given below and answer the following questions.

The given diagrams show the atomic structures of elements X and Y.

Question. Element X and Y could be _____ and _____respectively.
(a) Be and B
(b) C and O
(c) F and N
(d) C and N
Answer. D

Question.Valency of elements X and Y are respectively,
(a) 4 and 3
(b) 2 and 5
(c) 1 and 4
(d) 3 and 4
Answer. A

Question. Elements X and Y are
(a) isotopes
(b) isoelectronic
(c) isobars
(d) isomers.
Answer. C

Case IV : Read the passage given below and answer the following questions.

The mass of an atom is due to the masses of protons and neutrons in the nucleus. The relative masses of protons and neutrons are almost equal to one. Therefore, the atomic mass of an element should be nearly a whole number. But in many cases the atomic masses are fractional. The main reason for these fractional atomic masses is that these elements occur in nature as a mixture of several isotopes. The atomic mass of an element is the average of the atomic masses of these isotopes in the ratio of their proportion of occurrence.

Question. Chlorine occurs in nature in the form of two isotopes with atomic masses 35 u and 37 u in the ratio of 3 : 1 respectively. Atomic mass of chlorine is
(a) 35.5 u
(b) 34.5 u
(c) 35 u
(d) 36 u
Answer. A

Question. An element occurs in two isotopic forms with atomic masses 10 and 11. What is the percentage abundance of two isotopes in the sample having atomic mass 10.80?
(a) 20, 80
(b) 50, 50
(c) 25, 70
(d) 60, 40
Answer. A

Question. The fractional atomic masses of elements are due to the existence of
(a) isotopes having different masses
(b) diagonal relationship
(c) equal number of electrons and protons
(d) none of these.
Answer. A

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