Structure of Atom (Class 9 Science)
The atom consists of a nucleus containing protons and neutrons, surrounded by electrons in various shells. Understanding atomic structure is fundamental to
TL;DR: The atom consists of a nucleus containing protons and neutrons, surrounded by electrons in various shells. Understanding atomic structure is fundament…
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The atom consists of a nucleus containing protons and neutrons, surrounded by electrons in various shells. Understanding atomic structure is fundamental to
Structure of Atom MCQs with Answers & Explanations
Q1. Who proposed the nuclear model of the atom?
- Niels Bohr
- Ernest Rutherford ✓ (correct)
- J.J. Thomson
- Max Planck
Explanation: Rutherford's nuclear model proposed that the atom has a small, dense, positively charged nucleus surrounded by electrons.
Q2. The charge on an electron is:
- Can be either positive or negative
- Neutral
- Negative ✓ (correct)
- Positive
Explanation: An electron carries a negative charge equal to -1.6 × 10^-19 coulombs.
Q3. Which particles are present in the nucleus?
- Only protons
- Protons and electrons
- Only electrons
- Protons and neutrons ✓ (correct)
Explanation: The nucleus contains protons (positively charged) and neutrons (neutral). Electrons orbit around the nucleus.
Q4. An atom has 8 protons and 8 neutrons. What is its mass number?
- 16 ✓ (correct)
- 8
- 24
- 4
Explanation: Mass number = number of protons + number of neutrons = 8 + 8 = 16.
Q5. Isotopes are atoms that have:
- Same mass but different protons
- Same protons but different neutrons ✓ (correct)
- Different electrons and protons
- Same electrons but different protons
Explanation: Isotopes are atoms of the same element (same number of protons) but with different numbers of neutrons.
Q6. Bohr's model explains the stability of atoms by:
- Electrons moving randomly
- Electrons closer to nucleus are more stable
- Electron orbits in fixed energy levels ✓ (correct)
- Nucleus repelling electrons
Explanation: Bohr proposed that electrons occupy specific, quantized energy levels around the nucleus, and can jump between them by absorbing or emitting energy.
Q7. What is the maximum number of electrons in the second shell of an atom?
- 4
- 2
- 6
- 8 ✓ (correct)
Explanation: The second shell can hold a maximum of 8 electrons (2n^2 where n=2 gives 2×4 = 8).
Q8. The symbol X has atomic number 17 and mass number 35. How many neutrons does it have?
- 18 ✓ (correct)
- 35
- 17
- 52
Explanation: Number of neutrons = mass number - atomic number = 35 - 17 = 18.
Q9. Which of the following is a correct electron configuration for Oxygen (atomic number 8)?
- 4, 4
- 2, 6 ✓ (correct)
- 2, 4
- 2, 8
Explanation: Oxygen has 8 electrons. The first shell holds 2, and the remaining 6 go to the second shell, giving configuration 2, 6.
Q10. The nucleus accounts for most of the atom's:
- Electrons
- Charge
- Mass ✓ (correct)
- Volume
Explanation: Although the nucleus is tiny, it contains nearly all of the atom's mass due to the mass of protons and neutrons.
Frequently Asked Questions
What did Rutherford's gold foil experiment prove?
The experiment showed that most of the atom is empty space and the positive charge is concentrated in a small nucleus at the center, disproving Thomson's plum pudding model.
How do electrons gain energy to move to higher orbits in Bohr's model?
Electrons absorb specific amounts of energy (photons) equal to the energy difference between two orbits and jump to a higher energy level.
More Class 9 Science MCQs
- Light Reflection and Refraction
- Electricity
- Acids Bases and Salts
- Life Processes
- Carbon and its Compounds
- Metals and Non-metals
🤖 Stuck on any of these? Ask Syllab's free AI Tutor to explain step by step →