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Structure of the Atom — Class 9 CBSE Science MCQs with Solutions
Free Class 9 CBSE Science Structure of the Atom MCQs with step-by-step solutions. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — easy
Electron subatomic particle was discovered by:
A. E. Goldstein
B. J.J. Thomson ✓ Correct
C. James Chadwick
D. Ernest Rutherford
Solution: J.J. Thomson discovered electrons via cathode ray experiments.
Q2 — easy
Subatomic particle 'Neutron' carrying no charge was discovered by:
A. J.J. Thomson
B. Ernest Rutherford
C. James Chadwick ✓ Correct
D. Niels Bohr
Solution: James Chadwick discovered neutrons in 1932.
Q3 — easy
Alpha-particle scattering experiment led to the discovery of the:
A. Electron
B. Atomic Nucleus ✓ Correct
C. Neutron
D. Proton
Solution: Rutherford's gold foil experiment revealed the dense positive atomic nucleus.
Q4 — easy
Maximum capacity of electrons in the n-th energy shell is given by formula:
A. 2n
B. 2n² ✓ Correct
C. n²
D. 4n²
Solution: Bohr-Bury scheme states max electrons = 2n² (K=2, L=8, M=18, N=32).
Q5 — easy
Maximum number of electrons that can be accommodated in the outermost valence shell is:
A. 2
B. 8 ✓ Correct
C. 18
D. 32
Solution: Octet rule caps outermost shell capacity at 8 electrons.
Q6 — easy
Atomic number (Z) of an element equals total number of _______ in its nucleus.
A. Neutrons
B. Protons ✓ Correct
C. Protons + Neutrons
D. Electrons + Neutrons
Solution: Atomic number Z = number of protons.
Q7 — easy
Mass number (A) of an atom equals sum of number of:
A. Protons and Electrons
B. Protons and Neutrons (Nucleons) ✓ Correct
C. Neutrons and Electrons
D. Valence electrons
Solution: Mass Number A = Protons (Z) + Neutrons (N).
Q8 — easy
Atoms of same element having SAME atomic number but DIFFERENT mass numbers are:
A. Isobars
B. Isotopes ✓ Correct
C. Isotones
D. Polymers
Solution: Isotopes have same Z, different A (e.g. Protium, Deuterium, Tritium).
Q9 — easy
Atoms of different elements having DIFFERENT atomic numbers but SAME mass number are:
A. Isotopes
B. Isobars ✓ Correct
C. Allotropes
D. Isomers
Solution: Isobars have different Z, same A (e.g. ⁴⁰Ca₁₂ and ⁴⁰Ar₁₈).
Q10 — easy
Electronic configuration of Sodium (Atomic Number Z = 11) is:
A. 2, 8, 1 ✓ Correct
B. 2, 9
C. 2, 8, 2
D. 2, 8, 8, 1
Solution: K=2, L=8, M=1.
Q11 — easy
Valency of Chlorine (Z = 17, Configuration = 2, 8, 7) is:
A. 7
B. 1 ✓ Correct
C. 8
D. 2
Solution: 8 − 7 = 1 valence gain requirement.
Q12 — easy
Which isotope of Uranium is used as fuel in nuclear reactors?
A. U-238
B. U-235 ✓ Correct
C. U-234
D. U-239
Solution: Uranium-235 is used in nuclear power generation.
Q13 — easy
Isotope of Iodine is used in medical treatment of:
A. Cancer
B. Goitre ✓ Correct
C. Anemia
D. Diabetes
Solution: Iodine-131 isotope is used to treat goitre/thyroid disorders.
Q14 — easy
Isotope of Cobalt (Co-60) is used in medical treatment of:
A. Goitre
B. Cancer ✓ Correct
C. Malaria
D. Rickets
Solution: Cobalt-60 is used in radiotherapy for cancer treatment.
Q15 — easy
Who proposed discrete stationary orbits (energy levels) to explain atom stability?
A. J.J. Thomson
B. Rutherford
C. Niels Bohr ✓ Correct
D. Dalton
Solution: Niels Bohr proposed quantized planetary electron orbits.