Atomic Models — NEET Chemistry MCQs with Solutions
Free NEET Chemistry Atomic Models MCQs with step-by-step solutions (30 questions). Part of Atomic Structure. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Atomic Models · easy · theory
Thomson's model of the atom is popularly known as the:
A. Quantum model
B. Planetary model
C. Plum pudding model ✓ Correct
D. Nuclear model
Solution: Thomson pictured the atom as a sphere of positive charge with electrons embedded in it, like plums in a pudding (also called the watermelon model).
Q2 — Atomic Models · easy · theory
In Thomson's model, the electrons are:
A. Embedded in a sphere of uniform positive charge ✓ Correct
B. Present outside the atom
C. Revolving around a central nucleus
D. Located only at the centre of the atom
Solution: Thomson proposed a uniform sphere of positive charge with the negatively charged electrons studded throughout it, keeping the atom neutral.
Q3 — Atomic Models · easy · theory
In Rutherford's α-particle scattering experiment, the metal foil used was made of:
A. Gold ✓ Correct
B. Copper
C. Silver
D. Iron
Solution: Rutherford (with Geiger and Marsden) bombarded a very thin gold foil with α-particles.
Q4 — Atomic Models · easy · theory
In the α-scattering experiment, the observation that most α-particles passed straight through the foil showed that:
A. The atom is mostly empty space ✓ Correct
B. α-particles are negatively charged
C. The atom has a large negative core
D. The electrons are at the centre
Solution: Since the vast majority of α-particles went through undeflected, most of the atom's volume must be empty space.
Q5 — Atomic Models · medium · theory
The deflection of a small number of α-particles through large angles indicated the presence of:
A. A negatively charged centre
B. A uniform positive sphere
C. A small, dense, positively charged nucleus ✓ Correct
D. Free electrons in the atom
Solution: Large-angle deflections meant the positive charge and most of the mass are concentrated in a tiny central region — the nucleus.
Q6 — Atomic Models · medium · theory
That about 1 in 20,000 α-particles was deflected almost straight back suggests that the nucleus is:
A. Extremely small and very dense ✓ Correct
B. Large and diffuse
C. Spread throughout the atom
D. Negatively charged
Solution: Only a head-on approach to a tiny, massive, dense positive nucleus could reverse an α-particle, and such collisions are very rare.
Q7 — Atomic Models · easy · theory
The atomic number (Z) of an element is equal to the number of:
A. Protons in the nucleus ✓ Correct
B. Electrons in the outermost shell
C. Protons and neutrons
D. Neutrons in the nucleus
Solution: The atomic number Z is the number of protons in the nucleus (equal to the number of electrons in a neutral atom).
Q8 — Atomic Models · easy · theory
The mass number (A) of an atom is given by:
A. Number of protons only
B. Number of electrons + number of protons
C. Number of neutrons − number of protons
D. Number of protons + number of neutrons ✓ Correct
Solution: Mass number A = number of protons (Z) + number of neutrons (N). Neutrons = A − Z.
Q9 — Atomic Models · medium · numerical
The number of neutrons in ⁴⁰₂₀Ca is:
A. 18
B. 40
C. 20 ✓ Correct
D. 22
Solution: Neutrons = A − Z = 40 − 20 = 20.
Q10 — Atomic Models · medium · numerical
The number of neutrons present in ²³₁₁Na is:
A. 34
B. 23
C. 12 ✓ Correct
D. 11
Solution: Neutrons = A − Z = 23 − 11 = 12.
Q11 — Atomic Models · medium · numerical
The number of electrons in the ion ²⁴₁₂Mg²⁺ is:
A. 24
B. 14
C. 10 ✓ Correct
D. 12
Solution: A neutral Mg atom has 12 electrons; losing 2 to form Mg²⁺ leaves 12 − 2 = 10 electrons.
Q12 — Atomic Models · medium · numerical
The number of electrons in the chloride ion ³⁵₁₇Cl⁻ is:
A. 18 ✓ Correct
B. 16
C. 17
D. 35
Solution: A neutral Cl atom has 17 electrons; gaining 1 to form Cl⁻ gives 17 + 1 = 18 electrons.
Q13 — Atomic Models · easy · theory
Isotopes of an element have the same:
A. Atomic number but different mass number ✓ Correct
B. Number of neutrons
C. Mass number but different atomic number
D. Number of protons and neutrons
Solution: Isotopes have the same number of protons (same Z) but different numbers of neutrons, so different mass numbers.
Q14 — Atomic Models · easy · theory
Isobars are atoms that have the same:
A. Number of neutrons
B. Number of protons
C. Atomic number but different mass number
D. Mass number but different atomic number ✓ Correct
Solution: Isobars have the same mass number A but different atomic numbers Z (different elements).
Q15 — Atomic Models · medium · theory
Which of the following pairs represents isotopes?
A. ⁴⁰₁₈Ar and ⁴⁰₂₀Ca
B. ¹⁴₆C and ¹⁴₇N
C. ³⁵₁₇Cl and ³⁷₁₇Cl ✓ Correct
D. ²³₁₁Na and ²⁴₁₂Mg
Solution: Isotopes share the same atomic number. ³⁵Cl and ³⁷Cl both have Z = 17, differing only in neutrons.
Q16 — Atomic Models · medium · theory
Which of the following pairs represents isobars?
A. ¹²₆C and ¹³₆C
B. ³⁵₁₇Cl and ³⁷₁₇Cl
C. ⁴⁰₁₈Ar and ⁴⁰₂₀Ca ✓ Correct
D. ¹H and ²H
Solution: Isobars have the same mass number but different atomic numbers. ⁴⁰Ar (Z = 18) and ⁴⁰Ca (Z = 20) both have A = 40.
Q17 — Atomic Models · medium · theory
⁴⁰₁₈Ar, ⁴⁰₁₉K and ⁴⁰₂₀Ca are examples of:
A. Isobars ✓ Correct
B. Isotones
C. Isotopes
D. Isoelectronic species
Solution: All three have mass number 40 but different atomic numbers — they are isobars.
Q18 — Atomic Models · medium · theory
The species ¹₁H, ²₁H and ³₁H are:
A. Isotopes of hydrogen ✓ Correct
B. Isobars
C. Isotones
D. Different elements
Solution: Protium, deuterium and tritium all have Z = 1 but mass numbers 1, 2, 3 — isotopes of hydrogen.
Q19 — Atomic Models · medium · theory
Atoms having the same number of neutrons but different mass numbers are called:
A. Isotopes
B. Isotones ✓ Correct
C. Isoelectronic
D. Isobars
Solution: Isotones are atoms with the same number of neutrons (but different Z and A).
Q20 — Atomic Models · medium · theory
The pair ³⁰₁₄Si and ³¹₁₅P are examples of isotones because both have:
A. Mass number 30
B. 14 protons
C. 16 neutrons ✓ Correct
D. The same atomic number
Solution: Neutrons in Si = 30 − 14 = 16; neutrons in P = 31 − 15 = 16. Same neutron number ⇒ isotones.
Q21 — Atomic Models · easy · theory
The major drawback of Rutherford's nuclear model of the atom was that it could not explain the:
A. Stability of the atom ✓ Correct
B. Presence of electrons
C. Existence of the nucleus
D. Neutral nature of the atom
Solution: Rutherford's model could not account for why the revolving electron does not lose energy and collapse into the nucleus — i.e. atomic stability.
Q22 — Atomic Models · medium · theory
According to classical electromagnetic theory, an electron revolving around the nucleus should:
A. Continuously radiate energy and spiral into the nucleus ✓ Correct
B. Gain energy from the nucleus
C. Move away from the nucleus indefinitely
D. Remain in a fixed orbit forever
Solution: An accelerating (revolving) charged particle radiates energy; the electron should lose energy, spiral inward, and collapse into the nucleus — which does not happen.
Q23 — Atomic Models · medium · theory
Besides atomic stability, Rutherford's model also failed to explain the:
A. Neutrality of the atom
B. Charge on the electron
C. Line spectra of atoms ✓ Correct
D. Existence of protons
Solution: A continuously radiating electron would give a continuous spectrum, whereas atoms actually show discrete line spectra — which Rutherford's model could not explain.
Q24 — Atomic Models · easy · theory
The nucleus of an atom contains:
A. Protons and neutrons ✓ Correct
B. Protons and electrons
C. Only protons
D. Electrons and neutrons
Solution: The nucleus is made up of protons and neutrons (collectively called nucleons); electrons revolve around it.
Q25 — Atomic Models · medium · numerical
The diameter of a nucleus (~10⁻¹⁵ m) compared with that of the whole atom (~10⁻¹⁰ m) is smaller by a factor of about:
A. 10¹⁰
B. 10²
C. 10⁵ ✓ Correct
D. 10⁻⁵
Solution: (10⁻¹⁰)/(10⁻¹⁵) = 10⁵, so the atom is about 100,000 times larger in diameter than its nucleus.
Q26 — Atomic Models · medium · theory
In the gold foil experiment, the source of the α-particles was a:
A. Discharge tube
B. Radioactive substance ✓ Correct
C. Photocell
D. Heated tungsten filament
Solution: α-particles were emitted by a radioactive source (such as polonium/radium) and directed at the gold foil.
Q27 — Atomic Models · medium · theory
Thomson's plum pudding model was discarded mainly because it could not explain the:
A. Large-angle scattering of α-particles ✓ Correct
B. Charge on the electron
C. Existence of isotopes
D. Mass of the neutron
Solution: A uniform positive sphere (Thomson) would not deflect α-particles through large angles; the scattering results required a concentrated nucleus.
Q28 — Atomic Models · medium · theory
An atom is electrically neutral because it has:
A. More neutrons than protons
B. Equal numbers of protons and neutrons
C. Equal numbers of protons and electrons ✓ Correct
D. No charged particles
Solution: The positive charge of the protons is exactly balanced by the negative charge of an equal number of electrons.
Q29 — Atomic Models · easy · numerical
An element X has 17 protons and 18 neutrons. Its mass number is:
A. 35 ✓ Correct
B. 17
C. 1
D. 18
Solution: Mass number A = protons + neutrons = 17 + 18 = 35.
Q30 — Atomic Models · medium · numerical
For the ion ⁵⁶₂₆Fe³⁺, the numbers of protons, neutrons and electrons are respectively:
A. 30, 26, 23
B. 26, 30, 23 ✓ Correct
C. 26, 26, 30
D. 26, 30, 26
Solution: Protons = Z = 26; neutrons = 56 − 26 = 30; electrons = 26 − 3 = 23 (Fe³⁺ has lost 3 electrons).