Imp Questions For All Chapters – General Science Class 8
Short Questions
1. What is matter made of?
- Matter is made of atoms and molecules.
2. What is an atom?
- An atom is the smallest unit of an element that retains its properties.
3. Who discovered the electron?
- J.J. Thomson discovered the electron.
4. Where are protons and neutrons found in an atom?
- They are found in the nucleus of an atom.
5. What is the charge of a proton?
- A proton has a positive (+1) charge.
6. What is the charge of an electron?
- An electron has a negative (-1) charge.
7. What is the charge of a neutron?
- A neutron has no charge (neutral).
8. What is atomic number?
- Atomic number (Z) is the number of protons in an atom.
9. What is atomic mass number?
- Atomic mass number (A) is the total number of protons + neutrons in an atom.
10. What are isotopes?
- Isotopes are atoms of the same element with different mass numbers but the same atomic number.
11. What is valency?
- Valency is the number of bonds an atom can form to become stable.
12. What is Rutherford’s atomic model?
- Rutherford said that an atom has a small, dense nucleus with electrons revolving around it.
13. What is Bohr’s atomic model?
- Bohr said that electrons revolve in fixed orbits (shells) around the nucleus and do not lose energy.
14. What is a nuclear reactor?
- A machine that produces electricity using nuclear fission reactions.
15. What is the function of a moderator in a nuclear reactor?
- A moderator (heavy water or graphite) slows down neutrons to control nuclear reactions.
Long Questions
1. What is the difference between Thomson’s and Rutherford’s atomic models?
- Thomson’s Model: The atom is a sphere with positive charge spread everywhere and electrons embedded inside.
- Rutherford’s Model: The atom has a small nucleus with protons and electrons revolving around it in empty space.
2. How do electrons revolve around the nucleus in Bohr’s model?
- Bohr said that electrons move in fixed orbits (shells) at a certain distance from the nucleus.
- Each orbit has a specific energy, and electrons do not lose energy while moving in their orbit.
3. What is the difference between atomic number and mass number?
- Atomic number (Z) is the number of protons in an atom.
- Mass number (A) is the total number of protons + neutrons in an atom.
4. What are isotopes? Give an example.
- Isotopes are atoms of the same element with the same atomic number but different mass numbers.
- Example: Carbon has three isotopes – C-12, C-13, and C-14.
5. Why is an atom electrically neutral?
- An atom has equal numbers of protons (positive) and electrons (negative).
- Since positive and negative charges cancel each other, the atom remains neutral.
6. Why is Rutherford’s model not completely correct?
- According to physics, a charged particle (electron) moving in a circle should lose energy and fall into the nucleus.
- But atoms are stable, so Rutherford’s model could not explain this, which Bohr corrected later.
7. What happens in a nuclear reactor?
- A nuclear reactor uses uranium or thorium to produce energy through nuclear fission.
- The energy released is used to heat water, create steam, and generate electricity.
8. What are the main subatomic particles? Give their properties.
- Proton (+1 charge, in nucleus, mass = 1u)
- Neutron (neutral, in nucleus, mass = 1u)
- Electron (-1 charge, orbits nucleus, mass negligible)
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