Structure of Atom: Subatomic Particles MCQs Quiz | Class 9
This Class IX Science (Code 086) quiz focuses on Unit I: Matter – Its Nature and Behaviour. The topic covers the discovery, charge, and location of subatomic particles including electrons, protons, and neutrons. Test your understanding of atomic structure, review your score, and click “Download Answer PDF” to save the answer key for your exam preparation.
Understanding Subatomic Particles
In Class 9 Science, Unit I (Matter – Its Nature and Behaviour), we learn that atoms are not indivisible as Dalton suggested. Instead, they are composed of smaller subatomic particles: electrons, protons, and neutrons. These particles determine the mass, charge, and chemical properties of an atom.
1. Electrons (e–)
Discovered by J.J. Thomson through cathode ray experiments. Electrons are negatively charged particles located outside the nucleus in discrete orbits or shells. Their mass is considered negligible (about 1/2000 times that of a hydrogen atom).
2. Protons (p+)
The presence of positively charged radiations in a gas discharge was discovered by E. Goldstein in 1886. These were called canal rays. Protons are positively charged particles located inside the nucleus. The mass of a proton is taken as 1 unit (1 u).
3. Neutrons (n)
Discovered by J. Chadwick in 1932. Neutrons have no charge (they are neutral) and have a mass nearly equal to that of a proton. They are located inside the nucleus of all atoms (except hydrogen). The mass of an atom is primarily due to protons and neutrons.
Summary Table
| Particle | Symbol | Charge | Location | Discoverer |
|---|---|---|---|---|
| Electron | e– | Negative (-1) | Orbits | J.J. Thomson |
| Proton | p+ | Positive (+1) | Nucleus | E. Goldstein |
| Neutron | n | Neutral (0) | Nucleus | J. Chadwick |
Quick Revision Notes
- An atom as a whole is electrically neutral because the number of protons equals the number of electrons.
- The nucleus is positively charged due to protons.
- Electrons revolve rapidly around the nucleus in specific energy shells.
Extra Practice Questions
- What is the relative mass of a neutron compared to a proton? (Answer: Almost equal)
- Why was Thomson’s model compared to a Christmas pudding?
- If an atom contains 3 protons and 3 electrons, what is its total charge? (Answer: Zero/Neutral)
- Which subatomic particle is not present in a standard Hydrogen atom? (Answer: Neutron)
- What are Canal Rays? (Answer: Positively charged radiations)
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