🧪 Structure of the Atom – Class 9 Science MCQs

Section 2: Rutherford’s Model, Bohr’s Model & Neutrons (Q26–Q50)

Q26. Which statement best explains Rutherford’s nuclear model of the atom?

A. Electrons embedded in a positive sphere
B. Atom has a dense, positively charged nucleus
C. Electrons move randomly inside the atom
D. Atom is indivisible and indestructible

✅ Correct Answer: B. Atom has a dense, positively charged nucleus

Explanation:

• A. Electrons embedded in a sphere → Thomson’s model.
• B. Correct, Rutherford discovered nucleus from gold foil experiment.
• **C. Wrong, electrons revolve in orbits, not random.
• **D. Wrong, Dalton’s early theory.

Q27. Rutherford concluded that most of the atom is empty space because:

A. Electrons are very light
B. Most α-particles passed undeflected
C. Some α-particles bounced back
D. Nucleus is small

✅ Correct Answer: B. Most α-particles passed undeflected

Explanation:

• A. Light electrons → Not reason.
• B. Correct, undeflected passage meant empty space.
• **C. Bounce-back showed nucleus.
• **D. True but not reason for empty space.

Q28. In Rutherford’s model, electrons revolve around the nucleus similar to:

A. Earth around Sun
B. Wheel around axle
C. Planet around Moon
D. Cloud around mountain

✅ Correct Answer: A. Earth around Sun

Explanation:

• A. Correct, planetary model analogy.
• **B. Wrong analogy.
• **C. Wrong, moon revolves around earth.
• **D. Wrong.

Q29. Main drawback of Rutherford’s model:

A. Could not explain neutron
B. Could not explain isotopes
C. Could not explain stability of atom
D. Could not explain nucleus

✅ Correct Answer: C. Could not explain stability of atom

Explanation:

• **A. Neutrons discovered later, not major drawback.
• **B. Isotopes explained later.
• **C. Correct, electrons should lose energy & spiral into nucleus.
• **D. Nucleus was explained.

Q30. According to Bohr, electrons revolve in:

A. Fixed circular orbits of different energies
B. Random orbits
C. Elliptical orbits
D. Inside nucleus

✅ Correct Answer: A. Fixed circular orbits of different energies

Explanation:

• A. Correct, energy shells = quantised.
• **B. Wrong.
• **C. Wrong, elliptical orbit (later model, Sommerfeld).
• **D. Wrong.

Q31. The K, L, M, N shells can accommodate maximum electrons as per:

A. 2n
B. 2n²
C. 2n³
D. 2n⁴

✅ Correct Answer: B. 2n²

Explanation:

• A. 2n → Wrong.
• B. Correct, 2n² rule.
• **C. Wrong.
• **D. Wrong.

Q32. Maximum number of electrons in M shell (n=3):

A. 8
B. 18
C. 32
D. 2

✅ Correct Answer: B. 18

Explanation:

• Formula = 2n² = 2×3² = 18.
• **A. 8 → L shell.
• **B. Correct.
• **C. 32 → N shell.
• **D. 2 → K shell.

Q33. Which of the following is correct about neutrons?

A. Positively charged
B. Mass ~ proton, no charge
C. Negligible mass, no charge
D. Discovered by Rutherford

✅ Correct Answer: B. Mass ~ proton, no charge

Explanation:

• A. Positive → Wrong, protons are positive.
• B. Correct, neutron is neutral with ~1 u mass.
• **C. Wrong, neutron has mass equal to proton.
• **D. Wrong, discovered by Chadwick.

Q34. Who discovered neutron in 1932?

A. Rutherford
B. Chadwick
C. Moseley
D. Bohr

✅ Correct Answer: B. Chadwick

Explanation:

• A. Rutherford → Nucleus.
• B. Correct, James Chadwick.
• C. Moseley → Atomic number.
• D. Bohr → Energy levels.

Q35. Neutrons are present in the nucleus of:

A. All atoms
B. All atoms except hydrogen-1
C. All atoms except isotopes
D. Only metals

✅ Correct Answer: B. All atoms except hydrogen-1

Explanation:

• A. All atoms → Wrong, hydrogen-1 has no neutron.
• B. Correct.
• **C. Wrong, isotopes may have neutrons.
• **D. Wrong.

Q36. The nucleus of an atom contains:

A. Protons only
B. Neutrons only
C. Protons and neutrons
D. Electrons and neutrons

✅ Correct Answer: C. Protons and neutrons

Explanation:

• A. Protons only → Wrong.
• B. Neutrons only → Wrong.
• C. Correct, nucleons = protons + neutrons.
• **D. Electrons not inside nucleus.

Q37. Which is NOT true for Bohr’s atomic model?

A. Electrons revolve in discrete orbits
B. Each orbit has fixed energy
C. Energy is emitted when electron jumps between orbits
D. Electrons radiate energy while revolving

✅ Correct Answer: D. Electrons radiate energy while revolving

Explanation:

• A, B, C → True postulates.
• **D. Wrong, Bohr said no radiation in stable orbits.

Q38. The N shell (n=4) can accommodate maximum:

A. 8
B. 18
C. 32
D. 50

✅ Correct Answer: C. 32

Explanation:

• Formula = 2n² = 2×4² = 32.

Q39. If an element has atomic number 17, how many protons does it have?

A. 8
B. 17
C. 35
D. 18

✅ Correct Answer: B. 17

Explanation:

• Atomic number = protons = 17 (Chlorine).

Q40. For a neutral atom with Z=17, number of electrons = ?

A. 17
B. 18
C. 35
D. 16

✅ Correct Answer: A. 17

Explanation:

• Neutral atom → protons = electrons → 17.

Q41. Who proposed the concept of atomic number as number of protons?

A. Bohr
B. Rutherford
C. Moseley
D. Chadwick

✅ Correct Answer: C. Moseley

Explanation:

• A. Bohr → Energy levels.
• B. Rutherford → Nucleus.
• **C. Correct.
• D. Chadwick → Neutrons.

Q42. If atomic number = 6, mass number = 12, neutrons = ?

A. 6
B. 12
C. 18
D. 0

✅ Correct Answer: A. 6

Explanation:

• Mass number = protons + neutrons.
• Neutrons = 12 – 6 = 6.

Q43. Mass number of sodium (Na) if protons = 11, neutrons = 12:

A. 11
B. 12
C. 23
D. 22

✅ Correct Answer: C. 23

Explanation:

• Mass number = p + n = 11 + 12 = 23.

Q44. In Bohr’s model, energy is emitted/absorbed when:

A. Atom is at rest
B. Electron jumps between shells
C. Electrons radiate continuously
D. Protons move out of nucleus

✅ Correct Answer: B. Electron jumps between shells

Explanation:

• **A. Wrong.
• **B. Correct, quantum jumps emit/absorb photons.
• **C. Wrong, would destabilise atom.
• **D. Wrong, protons don’t move.

Q45. Which shell is filled first with electrons?

A. K shell
B. L shell
C. M shell
D. N shell

✅ Correct Answer: A. K shell

Explanation:

• Electrons fill lowest energy level first → K shell.

Q46. What is the maximum number of electrons in L shell (n=2)?

A. 2
B. 4
C. 6
D. 8

✅ Correct Answer: D. 8

Explanation:

• Formula = 2n² = 8 for L shell.

Q47. Which of the following elements has configuration 2, 8, 1?

A. Carbon
B. Sodium
C. Oxygen
D. Neon

✅ Correct Answer: B. Sodium

Explanation:

• **A. Carbon = 2,4.
• **B. Sodium (Z=11) = 2,8,1 → Correct.
• **C. Oxygen = 2,6.
• **D. Neon = 2,8.

Q48. Which of the following has configuration 2, 8, 7?

A. Oxygen
B. Nitrogen
C. Chlorine
D. Sodium

✅ Correct Answer: C. Chlorine

Explanation:

• **A. Oxygen = 2,6.
• **B. Nitrogen = 2,5.
• **C. Chlorine (Z=17) = 2,8,7 → Correct.
• **D. Sodium = 2,8,1.

Q49. Which is the correct electronic configuration of magnesium (Z=12)?

A. 2,8,2
B. 2,10
C. 12,0
D. 2,6,4

✅ Correct Answer: A. 2,8,2

Explanation:

• **A. Correct.
• **B. Wrong, can’t exceed 8 in L shell.
• **C. Wrong.
• **D. Wrong.

Q50. Which is the correct configuration for calcium (Z=20)?

A. 2,8,10
B. 2,8,8,2
C. 2,10,8
D. 2,18

✅ Correct Answer: B. 2,8,8,2

Explanation:

• **A. Wrong, L shell max 8.
• **B. Correct, Ca = 20 → 2,8,8,2.
• **C. Wrong, exceeds max distribution.
• **D. Wrong.

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