Chapter Exam

Chapter 4: Structure of the Atom — Online MCQ Test

Q: Who discovered the electron?

Answer: A. J. J. Thomson — J. J. Thomson discovered the electron through cathode ray experiments. This was one of the first proofs that atoms contain smaller charged particles.

Q: What is the charge of a proton?

Answer: C. Positive — A proton carries a positive charge. It is located in the nucleus of an atom.

Q: Which statement is true about Rutherford's atomic model?

Answer: B. Most of the atom is empty space — Rutherford's gold foil experiment showed that most of the atom is empty space. A small, dense, positively charged nucleus is present at the center.

Q: An element X has 12 electrons, 12 protons, and 13 neutrons. What is its mass number?

Answer: D. 25 — Mass number = number of protons + number of neutrons = 12 + 13 = 25. Electrons are not counted in mass number.

SCIENCE · CLASS 9th · Karnataka State Board

Practice Chapter 4: Structure of the Atom with a free chapter-wise online MCQ test for Karnataka State Board CLASS 9th SCIENCE. This chapter covers: This chapter details charged particles Thomson Rutherford Bohr atomic models subatomic particles atomic number mass number isotopes and isobars.. AI-generated questions from basic to board-exam level, with instant results and explanations.

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Chapter 4: Structure of the Atom — Important Questions & Answers (FAQ)

Frequently asked questions from Karnataka State Board CLASS 9th SCIENCE — Chapter 4: Structure of the Atom, with answers and explanations. These are sample questions; the exam has its own separate question set.

Who discovered the electron?

A. J. J. Thomson ✓
B. Ernest Rutherford
C. Niels Bohr
D. James Chadwick

Answer: A. J. J. Thomson
J. J. Thomson discovered the electron through cathode ray experiments. This was one of the first proofs that atoms contain smaller charged particles.

What is the charge of a proton?

A. Negative
B. No charge
C. Positive ✓
D. Depends on the atom

Answer: C. Positive
A proton carries a positive charge. It is located in the nucleus of an atom.

Which statement is true about Rutherford's atomic model?

A. Electrons are embedded in a positively charged sphere
B. Most of the atom is empty space ✓
C. Electrons have fixed circular orbits with fixed energies
D. The atom is indivisible

Answer: B. Most of the atom is empty space
Rutherford's gold foil experiment showed that most of the atom is empty space. A small, dense, positively charged nucleus is present at the center.

An element X has 12 electrons, 12 protons, and 13 neutrons. What is its mass number?

A. 12
B. 13
C. 24
D. 25 ✓

Answer: D. 25
Mass number = number of protons + number of neutrons = 12 + 13 = 25. Electrons are not counted in mass number.

Which statement best explains why isotopes of an element have nearly the same chemical properties?

A. They have the same number of neutrons
B. They have the same number of protons and electrons ✓
C. They have the same mass number
D. They occupy the same position in the periodic table because of different atomic numbers

Answer: B. They have the same number of protons and electrons
Chemical properties depend mainly on the electronic configuration, which is determined by the number of protons in a neutral atom. Isotopes have the same atomic number, so their chemical properties are nearly the same.

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