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1. Who discovered the subatomic particle called 'Electron'?
A. J.J. Thomson
B. Ernest Rutherford
C. James Chadwick
D. Niels Bohr
Answer: A. J.J. Thomson
Explanation: J.J. Thomson discovered the electron in 1897 through his cathode ray tube experiments.
2. Which subatomic particle was discovered by James Chadwick in 1932?
A. Electron
B. Proton
C. Neutron
D. Positron
Answer: C. Neutron
Explanation: James Chadwick discovered the neutral particle in the atomic nucleus called the neutron, which has mass nearly equal to a proton.
3. Rutherford's alpha-particle scattering experiment led to the discovery of:
A. Electron
B. Atomic Nucleus
C. Proton
D. Neutron
Answer: B. Atomic Nucleus
Explanation: Rutherford used gold foil and alpha particles to discover that most of an atom's mass and positive charge is concentrated in a tiny nucleus.
4. What is the maximum number of electrons that can be accommodated in the 'M' shell?
A. 2
B. 8
C. 18
D. 32
Answer: C. 18
Explanation: The maximum capacity of a shell is given by 2n². For the M shell (n = 3), capacity = 2 × 3² = 18 electrons.
5. The valency of Chlorine (Atomic Number = 17) is:
A. 7
B. 1
C. 8
D. 2
Answer: B. 1
Explanation: Chlorine's electronic configuration is 2, 8, 7. Since it needs 1 electron to complete its octet, its valency is 8 - 7 = 1.
6. Atoms of the same element having the same atomic number but different mass numbers are called:
A. Isobars
B. Isotopes
C. Isotones
D. Isomers
Answer: B. Isotopes
Explanation: Isotopes have identical atomic numbers (same protons) but different mass numbers (different neutrons), e.g., Protium, Deuterium, Tritium.
7. Which isotope of an element is used in the treatment of cancer?
A. Uranium-235
B. Cobalt-60
C. Iodine-131
D. Carbon-14
Answer: B. Cobalt-60
Explanation: An isotope of Cobalt (Cobalt-60) emits gamma rays and is widely used in radiotherapy for treating cancer.
8. What are Isobars?
A. Atoms with same atomic number and same mass number
B. Atoms with different atomic numbers but same mass number
C. Atoms with same neutrons but different protons
D. Atoms with same chemical properties
Answer: B. Atoms with different atomic numbers but same mass number
Explanation: Isobars are atoms of different elements having different atomic numbers but the same total mass number (e.g., Calcium-40 and Argon-40).
9. An atom has 11 protons and 12 neutrons. What is its mass number?
A. 11
B. 12
C. 23
D. 1
Answer: C. 23
Explanation: Mass Number (A) = Number of Protons + Number of Neutrons = 11 + 12 = 23 (Sodium, Na).
10. Who proposed that electrons move in discrete energy orbits (shells) around the nucleus?
A. J.J. Thomson
B. Ernest Rutherford
C. Niels Bohr
D. John Dalton
Answer: C. Niels Bohr
Explanation: Niels Bohr overcame Rutherford's model flaws by stating that electrons revolve in non-radiating discrete orbits named K, L, M, N shells.
This page contains a chapter-wise objective practice set. Try the questions without checking the answer first, then use the explanation to understand the point you missed. The current page contains 10 questions, so you can practise in smaller sets when you are revising.
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