Now we are in 4th chapter of NCERT book for CBSE. The chemistry chapter Structure Of The Atom is one of the most important chapter of class 9. In the end we have given a solution for exemplar and you must not ignore them.
30 MCQ Questions for Class 9 Science: Chapter 4 Structure Of The Atom
Question 1. Who discovered the electron?
a) Ernest Rutherford
b) J.J. Thomson
c) Neils Bohr
d) James Chadwick
Answer:
b) J.J. Thomson
Question 2. Which of the following is a limitation of Rutherford’s model of the atom?
a) It could not explain the stability of atoms
b) It did not mention neutrons
c) It considered electrons as stationary
d) It did not consider the nucleus
Answer:
a) It could not explain the stability of atoms
Question 3. According to Bohr’s model, electrons:
a) Move in random orbits around the nucleus
b) Revolve in fixed orbits around the nucleus
c) Are stationary inside the nucleus
d) Orbit the nucleus in elliptical orbits
Answer:
b) Revolve in fixed orbits around the nucleus
Question 4. The atomic number of an element is equal to the number of:
a) Protons in its nucleus
b) Neutrons in its nucleus
c) Electrons in its orbit
d) Protons and neutrons in its nucleus
Answer:
a) Protons in its nucleus
Question 5. Isotopes of an element have:
a) The same number of protons but different numbers of neutrons
b) Different numbers of protons but the same number of neutrons
c) The same number of protons and neutrons
d) Different numbers of protons and neutrons
Answer:
a) The same number of protons but different numbers of neutrons
Question 6. The mass number of an atom is determined by:
a) The total number of protons
b) The total number of electrons
c) The sum of the number of protons and neutrons
d) The sum of the number of protons and electrons
Answer:
c) The sum of the number of protons and neutrons
Question 7. Which of the following is true for isotopes?
a) They have identical physical properties
b) They have identical chemical properties
c) They have different atomic numbers
d) They are found in different periods of the periodic table
Answer:
b) They have identical chemical properties
Question 8. Valency of an element is related to:
a) The number of protons in its nucleus
b) The number of electrons in its outermost shell
c) The total number of shell electrons
d) The number of neutrons in its nucleus
Answer:
b) The number of electrons in its outermost shell
Question 9. Which of the following particles is present in the nucleus of an atom?
a) Electron
b) Proton
c) Neutron
d) Both b) and c)
Answer:
d) Both b) and c)
Question 10. Atoms having the same mass number but different atomic numbers are called:
a) Isotopes
b) Isobars
c) Isotones
d) Alloisomers
Answer:
b) Isobars
Question 11. What are canal rays?
a) Positively charged electrons
b) Negatively charged protons
c) Positively charged protons
d) Neutral neutrons
Answer:
c) Positively charged protons
Question 12. Which model of the atom proposed that atoms have their mass and positive charge concentrated in a small area?
a) J.J. Thomson’s model
b) Rutherford’s model
c) Bohr’s model
d) Dalton’s model
Answer:
b) Rutherford’s model
Question 13. The atomic number of an element is defined as:
a) The number of protons in its nucleus
b) The number of neutrons in its nucleus
c) The total number of nucleons
d) The number of electrons in its outermost shell
Answer:
a) The number of protons in its nucleus
Question 14. Which of the following is true about isotopes?
a) They have the same number of protons but different numbers of neutrons
b) They have different atomic numbers
c) They always have the same chemical properties
d) They are different elements
Answer:
a) They have the same number of protons but different numbers of neutrons
Question 15. What determines the valency of an element?
a) The number of protons in its nucleus
b) The number of neutrons in its nucleus
c) The number of electrons in its outermost shell
d) The total number of electron shells
Answer:
c) The number of electrons in its outermost shell
Question 16. How many electrons are there in the outermost shell of an atom with atomic number 17?
a) 5
b) 7
c) 8
d) 17
Answer:
b) 7
Question 17. Which subatomic particle was discovered by J. Chadwick?
a) Electron
b) Proton
c) Neutron
d) Positron
Answer:
c) Neutron
Question 18. The mass number of an atom is equal to:
a) The number of protons
b) The number of electrons
c) The number of protons plus the number of neutrons
d) The number of protons plus the number of electrons
Answer:
c) The number of protons plus the number of neutrons
Question 19. Which of the following correctly represents the electronic configuration of nitrogen (Atomic number = 7)?
a) 2, 5
b) 2, 4, 1
c) 2, 2, 3
d) 7
Answer:
a) 2, 5
Question 20. Atoms with the same atomic number but different mass numbers are called:
a) Isotopes
b) Isobars
c) Isotones
d) Alloisomers
Answer:
a) Isotopes
Question 21. The mass of a neutron is almost equal to the mass of a __________.
Fill in the blank.
Answer:
Proton
Question 22. The total number of protons and neutrons in the nucleus of an atom is known as its __________.
Fill in the blank.
Answer:
Mass number
Question 23. __________ discovered the proton in an atom.
Fill in the blank.
Answer:
Ernest Rutherford
Question 24. Atoms of the same element with different mass numbers are called __________.
Fill in the blank.
Answer:
Isotopes
Question 25. The outermost shell of an atom cannot have more than __________ electrons.
Fill in the blank.
Answer:
8
Question 26. Electrons are present in the nucleus of an atom. (True/False)
True / False
Answer:
False
Question 27. Isobars are atoms of different elements with the same atomic number. (True/False)
True / False
Answer:
False
Question 28. Neutrons do not carry any charge and are neutral. (True/False)
True / False
Answer:
True
Question 29. The valency of an element is determined by the number of valence electrons in its atom. (True/False)
True / False
Answer:
True
Question 30. Atoms combine in the ratio of their atomic numbers to form compounds. (True/False)
True / False
Answer:
False
Question on Match the Columns
Unmatched Columns – Questions
| Column A | Column B |
|---|---|
| (i) Thomson’s Atomic Model | (a) Nucleus with protons and neutrons |
| (ii) Rutherford’s Atomic Model | (b) Electrons in fixed orbits |
| (iii) Bohr’s Atomic Model | (c) Electrons embedded in a positively charged sphere |
| (iv) Neutron discovery | (d) J.J. Thomson |
| (v) Proton discovery | (e) Scattering experiment with alpha particles |
| (vi) Electron discovery | (f) J. Chadwick |
Matched Columns – Answer
| Column A | Column B |
|---|---|
| (i) Thomson’s Atomic Model | (c) Electrons embedded in a positively charged sphere |
| (ii) Rutherford’s Atomic Model | (e) Scattering experiment with alpha particles |
| (iii) Bohr’s Atomic Model | (b) Electrons in fixed orbits |
| (iv) Neutron discovery | (f) J. Chadwick |
| (v) Proton discovery | (a) Nucleus with protons and neutrons |
| (vi) Electron discovery | (d) J.J. Thomson |
MCQ questions from Exemplar Problems
Question 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
Answer:
b) 2, 8, 2
Question 2. Rutherford’s ‘alpha (α) particles scattering experiment’ resulted in discovery of
a) Electron
b) Proton
c) Nucleus in the atom
d) Atomic mass
Answer:
c) Nucleus in the atom
Question 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) ³¹₁₅X
b) ³¹₁₆X
c) ¹⁶₁₅X
d) ¹⁵₁₆X
Answer:
a) ³¹₁₅X — Atomic number = electrons = 15; mass number = protons + neutrons = 15 + 16 = 31.
Question 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)
Answer:
d) (i), (ii) and (iv) — Radioactivity was not explained by Dalton’s theory.
Question 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)
Answer:
a) (i) and (iii)
Question 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)
Answer:
d) (ii) and (iv)
Question 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 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) (i), (ii) and (iii)
Question 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)
Answer:
b) (ii) and (iv)
Question 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
Answer:
b) 10 — Protons = 27 − 14 = 13; a 3+ ion has 3 fewer electrons than protons, so electrons = 13 − 3 = 10.
Question 10. Identify the Mg²⁺ ion from Fig. 4.1 where, n and p represent the number of neutrons and protons respectively
a) (a)
b) (b)
c) (c)
d) (d)
Answer:
d) (d) — Mg has p = 12; Mg²⁺ has 10 electrons (2, 8). Diagram (d) shows p = 12 with two shells having 2 and 8 electrons.
