Class 9 Chemistry MCQs: Atomic Structure

MCQs (sample)

Showing 25 questions from this chapter. For a full timed test, use “Start online test”.

1. 1. What does the term 'isotope' refer to?

   • Atoms of the same element with the same atomic number and different mass numbers
   • Atoms of different elements with the same mass number
   • Atoms of the same element with different atomic numbers
   • Atoms with different chemical properties
   Answer & explanation

   Correct: Atoms of the same element with the same atomic number and different mass numbers

   Isotopes are defined as atoms of the same element that have the same atomic number but different mass numbers.

2. 2. What is the term used to describe the arrangement of electrons in sub-shells?

   • Electronic configuration
   • Atomic structure
   • Chemical bonding
   • Mass number
   Answer & explanation

   Correct: Electronic configuration

   The arrangement of electrons in sub-shells is called the electronic configuration.

3. 3. What does the proton number indicate about an element?

   • The number of protons in the nucleus
   • The total mass of the atom
   • The number of neutrons in the atom
   • The color of the element
   Answer & explanation

   Correct: The number of protons in the nucleus

   The proton number indicates the number of protons in the nucleus of an atom.

4. 4. What are cations?

   • Positively charged ions formed when an atom loses electrons
   • Negatively charged ions formed when an atom gains electrons
   • Neutral atoms with equal protons and electrons
   • Ions formed from non-metals
   Answer & explanation

   Correct: Positively charged ions formed when an atom loses electrons

   Cations are defined as positively charged ions that form when an atom loses one or more electrons.

5. 5. What is the relative charge of a neutron?

   • 0 (neutral)
   • +1
   • -1
   • 1.6726 x 10^-27 kg
   Answer & explanation

   Correct: 0 (neutral)

   Neutrons have a relative charge of 0, meaning they are neutral particles.

6. 6. Who was the first to provide quantitative information about atomic masses?

   • Dalton
   • Einstein
   • Curie
   • Bohr
   Answer & explanation

   Correct: Dalton

   Dalton was one of the first chemists to provide quantitative information about atomic masses.

7. 7. What is the main postulate of Dalton's atomic theory regarding elements?

   • All elements are composed of tiny indivisible particles called atoms.
   • Atoms can be created and destroyed.
   • Atoms have different masses and volumes.
   • Atoms are visible to the naked eye.
   Answer & explanation

   Correct: All elements are composed of tiny indivisible particles called atoms.

   Dalton's atomic theory states that all elements are composed of tiny indivisible particles called atoms.

8. 8. Which of the following is the isotopic symbol for Deuterium?

   • D
   • T
   • H
   • C
   Answer & explanation

   Correct: D

   Deuterium is represented by the symbol D.

9. 9. Which shell corresponds to n=2?

   • L shell
   • K shell
   • M shell
   • N shell
   Answer & explanation

   Correct: L shell

   For n=2, it corresponds to the L shell.

10. 10. In a neutral atom, how do the number of protons compare to the number of electrons?

    • They are equal
    • Protons outnumber electrons
    • Electrons outnumber protons
    • They are always different
    Answer & explanation

    Correct: They are equal

    In neutral atoms, the number of protons is equal to the number of electrons, balancing their charges.

11. 11. How is a cation formed?

    • When an atom gains electrons
    • When an atom loses one or more electrons
    • By splitting a neutral atom
    • When an atom undergoes a chemical reaction
    Answer & explanation

    Correct: When an atom loses one or more electrons

    A cation is formed when an atom loses one or more electrons.

12. 12. Which subatomic particle has a negative charge?

    • Proton
    • Neutron
    • Electron
    • None of the above
    Answer & explanation

    Correct: Electron

    Electrons carry a negative charge.

13. 13. Which isotope of carbon is used as the standard for atomic mass?

    • C-12
    • C-14
    • C-11
    • C-13
    Answer & explanation

    Correct: C-12

    The light isotope of carbon C-12 has been chosen as the standard for atomic mass.

14. 14. What did Rutherford's experiment demonstrate about the structure of the atom?

    • Most of the space in an atom is empty.
    • Atoms are made entirely of protons.
    • Electrons are distributed throughout the nucleus.
    • Atoms contain only neutrons.
    Answer & explanation

    Correct: Most of the space in an atom is empty.

    Rutherford's experiment showed that most of the space occupied by an atom is empty, as most alpha particles passed through the foil undeflected.

15. 15. What percentage of naturally occurring hydrogen is comprised of Protium?

    • 0.0015%
    • 99.99%
    • 1.1%
    • 75%
    Answer & explanation

    Correct: 99.99%

    Naturally occurring hydrogen contains 99.99% Protium (Hydrogen-1).

16. 16. How many sub-shells does the L shell have?

    • 1
    • 2
    • 3
    • 4
    Answer & explanation

    Correct: 2

    The L shell (n=2) has two sub-shells, which are 2s and 2p.

17. 17. Which element has a proton number of 6?

    • Carbon
    • Oxygen
    • Nitrogen
    • Sodium
    Answer & explanation

    Correct: Carbon

    An atom with a proton number of 6 must be carbon.

18. 18. What happens to the electron configuration of an atom when it becomes a cation?

    • It becomes more negative
    • It achieves a configuration similar to noble gases
    • It remains unchanged
    • It loses protons
    Answer & explanation

    Correct: It achieves a configuration similar to noble gases

    The resulting cation has the electronic configuration of a noble gas after losing electrons.

19. 19. Where are protons and neutrons located in an atom?

    • In the energy levels
    • In the electron cloud
    • In the nucleus
    • Free in space
    Answer & explanation

    Correct: In the nucleus

    Protons and neutrons are located in the nucleus of an atom.

20. 20. What is the relative atomic mass of hydrogen?

    • 1.008 amu
    • 2.016 amu
    • 8.40 amu
    • 12.000 amu
    Answer & explanation

    Correct: 1.008 amu

    The relative atomic mass of hydrogen has been calculated as 1.008 amu based on its mass relative to C-12.

21. 21. What does Rutherford's planetary model suggest?

    • Electrons revolve around the nucleus in fixed orbits.
    • Electrons are found in a cloud-like region around the atom.
    • The nucleus contains no protons.
    • Atoms have no mass.
    Answer & explanation

    Correct: Electrons revolve around the nucleus in fixed orbits.

    Rutherford proposed a planetary model where electrons revolve around the nucleus in orbits, similar to planets around the sun.

22. 22. What unique property does Tritium have?

    • It is the most abundant isotope of hydrogen.
    • It is radioactive and rare.
    • It has no neutrons.
    • It is used to trace blood flow.
    Answer & explanation

    Correct: It is radioactive and rare.

    Tritium is radioactive and is not commonly found in nature.

23. 23. Which of the following sub-shell can accommodate a maximum of 10 electrons?

    • 2p
    • 3d
    • 4f
    • 1s
    Answer & explanation

    Correct: 3d

    The d sub-shell can accommodate a maximum of 10 electrons.

24. 24. What is the term used for the total number of protons and neutrons in an atom?

    • Atomic number
    • Mass number
    • Proton number
    • Charge number
    Answer & explanation

    Correct: Mass number

    The total number of protons and neutrons is known as its mass number or nucleon number.

25. 25. Which of the following is an example of a cation?

    • O-2
    • Na+
    • F-
    • Cl-
    Answer & explanation

    Correct: Na+

    Na+ is an example of a cation formed when sodium loses its valence electron.