MCQs For Class 9 Science- Structure of Atom

Structure Of Atom

1. 1. Which 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
      Ans: d
      Explanation: The atomic number of sodium is 11. Hence, its electronic configuration is 2,8,1
   2. Rutherford’s alpha particle scattering experiment was responsible for the discovery of:
      a) Atomic Nucleus
      b) Electron
      c) Proton
      d) Neutron
      Ans: a
      Explanation: According to Rutherford’s experiment, Rutherford predicted that the centre part of the atom is positively charged and is responsible for the mass of the atom. He called these protons an atomic nuclei.
   3. If Z=3 what would be the valency of the element? Also, name the element.
      Electronic Configuration of an element.
      Z=3  = K     L
      2,     1
      Valancy of the element= Number of valence electron
      =  1
      Name of the element= (Li)
   4. Find the number of a solid non-metal with valency 3.
      a) 4
      b) 8
      c) 15
      d)14
      Ans: c
      Explanation: Configuration of 15= 2,8,5
      It only is able to form valancy=3
   5. 1H1 is named as
      a) Proton
      b) Deutrium
      c) Tritium
      d) Proton
      Ans: a
      Explanation: The name of 1H1 is the protium.
   6. Who amended Rutherford’s shortcomings?
      a) Dalton
      b) James Chadwick
      c) Neil’s Bohr
      d) J.J Thomson
      Ans: c
      Explanation: Neils’Bohr amended Rutherford’s shortcomings.
   7. The number of electrons the K-shell and L-shell can accommodate:
      a) 8,2
      b) 2,8
      c) 8,8
      d) 2,2
      Ans: b
      Explanation: According to Bohr’s rule 2n2, the first shell or K-shell accommodates 2 electrons and the second shell or L-shell should accommodate 8 electrons.
   8. There are 15 protons and 16 neutrons in the nucleus of an element. calculate its atomic number and its atomic mass.
      a) 30
      b) 31
      c) 32
      d) 33
      Ans: b
      Explanation: Atomic Number= Number of proton=15
      Atomic Mass = Number of proton+Number of Neutron
      = 15+16  = 31
   9. The charge on an electron is equal to:
      a) 1.6 x10-19 C of -ve charge
      b) 1.6 x 10 -22 of -ve charge
      c) 2.6 x 10-19 of -ve charge
      d) 1.6 x 10-23 C of -ve charge
      Ans: a
      Explanation: The charge of an electron is 1.6 x 10-19 C.
   10. The mass of a proton is:
       a) 1.000 amu
       b) 0.9073 amu
       c) 1.0073 amu
       d) 5.486 x 10-4 amu
       Ans: c
       Explanation: The mass of a proton is 1.0073 amu.
   11. Which of the following statement about the electron is incorrect?
       a) The mass of the electron is equal to the mass of the neutron.
       b) It is a basic constituent of all atoms.
       c) It is a constituent of cathode rays.
       d) It is a negatively charged particle.
       Ans: a
       Explanation: The mass of an electron is equal to 1/1836 of the mass of proton or neutron.
   12. 7 N 15 and 8 O 16 are pair of:
       a) Isotopes
       b) Isobars
       c) Isotones
       d) None of these
       Ans: c
       Explanation: 7 N 15 and 8 O 16 are pairs of isotones. Isotones are atomic species that share the same number of neutrons and differ in the number of protons. In the case of 7 N 15( Number of proton=7, number of neutron=8) 8 O 16 ( Number of proton=8, Number of neutron=8)
   13. What was the source of alpha particles in the Rutherford scattering experiment?
       a) Hydrogen nucleus
       b) Argon nucleus
       c) Helium Nucleus
       d) None of these
       Ans: c
       Explanation:
   14. Why was Thomson’s model of an atom failed?
       1) It could not explain the screening of negative charges from that of positive
       2) It did not tell about the presence f electron
       c) It did not give an idea about the discrete energy levels
       d) It explained the atom as a whole to be electrically neutral
       Choose the correct option from the following:
       a) Only 3)
       b) Both 1) and 3)
       c) Only 1)
       d) Both 2) and 4)
       Ans: Both 1) and 3)
       Explanation:
   15. 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) 15 X31
       b) 16X31
       c) 15X16
       d) 16X15
       Ans: a
       Explanation: Given that, the number of electrons in element X=15 and the number of neutrons=16. Atomic number= Number of protons +Number of electrons in neutral atom=15
       Mass number= number of protons+number of neutrons=15+16=31

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