CUET UG Physics Booster Test 2-Early Atomic Theory -

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CUET UG Physics Booster Test 2-Early Atomic Theory

⏱️ 30 Minutes

❓ 20 Questions

📌 Answers are locked once submitted — results and explanations appear at the end.

CUET UG Physics Booster Test 2-Early Atomic Theory

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QUESTION 1 OF 20

Which of the following is correct regarding J.J. Thomson's experiment and its conclusion?

Answer Review

1 Which of the following is correct regarding J.J. Thomson's experiment and its conclusion?

A Electric discharge through gases proved that atoms of all elements have distinct, unique negatively charged constituents.

B The identical nature of electrons in different atoms suggests they are a fundamental constituent of all matter.

C The experiments directly revealed the presence of a heavy central positive nucleus.

D It proved that matter continuously emits discrete electromagnetic radiation.

💡 Short Explanation

�� Cathode rays were identical regardless of the gas used. �� Electrons are present in all atoms. �� Thomson discovered a universal negatively charged particle.

✅ Correct Answer Explanation

Thomson's discharge tube experiments showed that cathode rays possess identical properties irrespective of the gas or electrode material used. This indicated that electrons are common constituents of all atoms and therefore fundamental components of matter. Thus, option B correctly states the conclusion drawn from Thomson's experiments.

❓ Why Other Options Are Incorrect

�� Option A → Incorrect because electrons were found to be identical, not distinct for each element.
�� Option C → Incorrect because the nucleus was discovered later by Rutherford.
�� Option D → Incorrect because Thomson's experiment was unrelated to electromagnetic radiation spectra.

🎯 Strategy

Used

Elimination

Application:

Reject statements describing discoveries made by other scientists or unrelated phenomena.

Final Logic:

The universality of electrons supports option B.

🧠 Memory Trick

Same Electron → Same Matter

📚 Class XII – NCERT Chemistry Part I – Chapter: Structure of Atom – Topic: Thomson's Discovery of Electron

2 To maintain macroscopic stability, the atom's overall charge and the internal particles responsible for balancing negative charges are respectively:

A Electrically neutral, Positive charges

B Positively charged, Electrons

C Electrically neutral, Neutrons

D Negatively charged, Positive charges

💡 Short Explanation

�� Ordinary matter is neutral. �� Positive charges balance electrons. �� Neutrality maintains stability.

✅ Correct Answer Explanation

Atoms are electrically neutral under normal conditions because the total positive charge balances the total negative charge of electrons. The positive charge present within the atom neutralizes the electron charge and ensures macroscopic neutrality. Therefore, option A is correct.

❓ Why Other Options Are Incorrect

�� Option B → Incorrect because atoms are generally not positively charged.
�� Option C → Incorrect because neutrons are electrically neutral.
�� Option D → Incorrect because atoms are not normally negatively charged.

🎯 Strategy

Used

Contextual/Tonal Matching

Application:

Match atomic neutrality with the charge balancing mechanism.

Final Logic:

Positive charges balance electrons to maintain neutrality.

🧠 Memory Trick

Neutral Atom = Positive + Negative

📚 Class XII – NCERT Chemistry Part I – Chapter: Structure of Atom – Topic: Electrical Neutrality of Atom

3 Incorrect statement about the mass and charge distribution in Thomson's model:

A Positive charge occupies the entire volume of the atom uniformly.

B It implies a continuous mass distribution throughout the atomic volume.

C It provides a dynamically stable system against electrostatic collapse.

D Electrons are embedded like seeds rather than orbiting a central mass.

💡 Short Explanation

�� Thomson proposed embedded electrons. �� Positive charge filled the atom uniformly. �� Stability was not satisfactorily explained.

✅ Correct Answer Explanation

Although Thomson's model assumed electrons embedded within a positively charged sphere, it failed to provide a convincing explanation for atomic stability. The model could not adequately explain the behavior of electrons and later experimental observations. Hence, option C is correct.

❓ Why Other Options Are Incorrect

�� Option A → Correct feature of Thomson's model.
�� Option B → Correct because positive charge and mass were assumed to be spread throughout the atom.
�� Option D → Correct because electrons were embedded, not orbiting.

🎯 Strategy

Used

Odd One Out

Application:

Identify the statement not supported by Thomson's model.

Final Logic:

Atomic stability remained an unresolved issue in the model.

🧠 Memory Trick

Thomson = Embedded, Not Stable

📚 Class XII – NCERT Chemistry Part I – Chapter: Structure of Atom – Topic: Limitations of Thomson's Model

4 Statements about the structural logic of the plum pudding model:
1. Electrons act like seeds embedded in a positive sphere.
2. The arrangement provides total neutralization of atomic charge.
3. It correctly predicted the large-angle scattering of alpha particles.
4. It was proposed prior to the alpha-particle scattering experiment.

A (1), (2), (4)

B (1), (3), (4)

C (2), (3)

D (1), (2), (3)

💡 Short Explanation

�� Electrons were embedded. �� Total charge remained neutral. �� Model failed for scattering results.

✅ Correct Answer Explanation

Statement 1 is correct because electrons were embedded within a positively charged sphere. Statement 2 is correct because positive and negative charges balanced each other. Statement 3 is incorrect because Thomson's model could not explain large-angle alpha-particle scattering. Statement 4 is correct because the model existed before Rutherford's scattering experiment. Therefore, statements 1, 2 and 4 are correct.

❓ Why Other Options Are Incorrect

�� Option B → Includes statement 3, which is incorrect.
�� Option C → Includes statement 3 and omits statement 1.
�� Option D → Includes statement 3, which is incorrect.

🎯 Strategy

Used

Elimination

Application:

Test each statement against Rutherford's experimental findings.

Final Logic:

Only statements 1, 2 and 4 are valid.

🧠 Memory Trick

Seeds in Pudding Before Scattering

📚 Class XII – NCERT Chemistry Part I – Chapter: Structure of Atom – Topic: Plum Pudding Model

5 Subsequent studies evaluating the distribution of charges within the atom showed that

A the plum pudding model perfectly predicted the electrostatic equilibrium of embedded electrons

B the actual distribution of electrons and positive charges is very different from Thomson's uniform assumption

C positive charge is spread evenly while electrons orbit at large distances

D the mass is uniformly distributed but the charge is entirely concentrated

💡 Short Explanation

�� Rutherford challenged Thomson's model. �� Positive charge is concentrated. �� Charge distribution is not uniform.

✅ Correct Answer Explanation

Rutherford's scattering experiments demonstrated that positive charge and most of the atomic mass are concentrated in a very small nucleus. This finding differed greatly from Thomson's assumption of a uniform positive charge distribution. Thus, option B is correct.

❓ Why Other Options Are Incorrect

�� Option A → Incorrect because Thomson's model failed experimentally.
�� Option C → Incorrect because positive charge is not uniformly spread.
�� Option D → Incorrect because mass is also concentrated in the nucleus.

🎯 Strategy

Used

Elimination

Application:

Compare Thomson's model with Rutherford's findings.

Final Logic:

Experiments showed a radically different charge distribution.

🧠 Memory Trick

Rutherford Changed Thomson

📚 Class XII – NCERT Chemistry Part I – Chapter: Structure of Atom – Topic: Rutherford Model

6 Statements about alpha-particle scattering:
1. Most alpha particles pass through without deflection.
2. Large angle deflection occurs for all interacting particles.
3. A small fraction deflects by more than 90 degrees.
4. Scattering data contradicted Thomson's uniform mass distribution.

A (1), (3), (4)

B (1), (2), (3)

C (2), (3), (4)

D (1), (2), (4)

💡 Short Explanation

�� Most alpha particles passed straight through. �� Few suffered large deflections. �� Results disproved Thomson's model.

✅ Correct Answer Explanation

Statement 1 is correct because most of the atom is empty space. Statement 2 is incorrect because only a very small fraction experienced large-angle scattering. Statement 3 is correct because some particles were deflected through angles greater than 90°. Statement 4 is correct because the observations contradicted uniform charge and mass distribution. Therefore, statements 1, 3 and 4 are correct.

❓ Why Other Options Are Incorrect

�� Option B → Includes statement 2, which is incorrect.
�� Option C → Includes statement 2, which is incorrect.
�� Option D → Includes statement 2, which is incorrect.

🎯 Strategy

Used

Elimination

Application:

Evaluate each statement using Rutherford's observations.

Final Logic:

Only statements 1, 3 and 4 agree with experimental results.

🧠 Memory Trick

Most Straight, Few Scatter

📚 Class XII – NCERT Chemistry Part I – Chapter: Structure of Atom – Topic: Alpha-Particle Scattering Experiment

7 Match List I with List II for radiation types

List I	List II
1. Solids and liquids	a. Electrically excited discrete lines
2. Rarefied gases in a flame	b. Thermally excited discrete lines
3. Neon sign	c. Continuous spectrum (condensed phase)
4. Dense gases	d. Continuous spectrum (gas phase)

A (1)-c, (2)-b, (3)-a, (4)-d

B (1)-a, (2)-b, (3)-c, (4)-d

C (1)-d, (2)-c, (3)-b, (4)-a

D (1)-c, (2)-d, (3)-a, (4)-b

💡 Short Explanation

�� Solids and liquids give continuous spectra. �� Flame-excited gases give line spectra. �� Neon signs produce electrically excited lines.

✅ Correct Answer Explanation

1 → c : Solids and liquids emit continuous spectra. 2 → b : Rarefied gases heated in a flame emit thermally excited line spectra. 3 → a : Neon signs emit electrically excited discrete spectral lines. 4 → d : Dense gases can produce continuous spectra. Therefore, option A is correct.

❓ Why Other Options Are Incorrect

�� Option B → Incorrect matching for solids and liquids.
�� Option C → Multiple pairings are incorrect.
�� Option D → Dense gases are incorrectly matched.

🎯 Strategy

Used

Option Grouping

Application:

Match each source with its characteristic spectrum.

Final Logic:

Only option A correctly matches all pairs.

🧠 Memory Trick

Solid-Continuous, Flame-Thermal, Neon-Electric

📚 Class XII – NCERT Physics Part II – Chapter: Atoms – Topic: Continuous and Line Spectra

8 In condensed matter, the emission of a continuous distribution of several wavelengths is primarily due to

A the isolated nature of atoms resulting in unchanged energy levels

B the interaction of each atom or molecule with its neighbours

C the strict quantization of angular momentum in dense media

D the total reflection of light within the solid structure

💡 Short Explanation

�� Neighbouring particles interact strongly. �� Energy levels broaden. �� Continuous spectra result.

✅ Correct Answer Explanation

In condensed matter, atoms and molecules are closely packed and interact strongly with neighbouring particles. These interactions broaden the energy states and produce a continuous spectrum rather than discrete lines. Hence, option B is correct.

❓ Why Other Options Are Incorrect

�� Option A → Incorrect because atoms are not isolated.
�� Option C → Incorrect because angular momentum quantization is not the reason for continuous spectra.
�� Option D → Incorrect because reflection does not create continuous emission spectra.

🎯 Strategy

Used

Contextual/Tonal Matching

Application:

Identify the physical cause of continuous emission.

Final Logic:

Neighbour interactions produce continuous spectra.

🧠 Memory Trick

Close Neighbours → Continuous Spectrum

📚 Class XII – NCERT Physics Part II – Chapter: Atoms – Topic: Continuous Spectra

9 If an atomic nucleus has a charge of x e and its electron cloud has an effective charge of -y e, what is the expression for the net charge of this atom?

A -(x + y) e

B (x + y) e

C (x - y) e

D (y - x) e

💡 Short Explanation

�� Nuclear charge is positive. �� Electron cloud charge is negative. �� Net charge is the algebraic sum.

✅ Correct Answer Explanation

The nucleus contributes +xe and the electron cloud contributes −ye. Net charge = xe − ye = (x − y)e. Therefore, option C is correct.

❓ Why Other Options Are Incorrect

�� Option A → Adds charges incorrectly.
�� Option B → Treats both charges as positive.
�� Option D → Gives the opposite sign.

🎯 Strategy

Used

Substitution

Application:

Substitute positive and negative charge values into the expression.

Final Logic:

(+xe) + (−ye) = (x − y)e.

🧠 Memory Trick

Positive Minus Negative

📚 Class XII – NCERT Chemistry Part I – Chapter: Structure of Atom – Topic: Net Atomic Charge

10 Which of the following is correct about electrical excitation in a glow tube?

A It produces a continuous spectrum due to close atomic spacing.

B The large average spacing between atoms ensures emission is characteristic of individual atoms.

C It confirms that all elements emit identical spectral lines when ionized.

D It works on the principle of radioactive alpha emission.

💡 Short Explanation

�� Glow tubes contain rarefied gases. �� Atoms are widely separated. �� Emission comes from individual atoms.

✅ Correct Answer Explanation

In glow tubes, gases are maintained at low pressure, resulting in large average spacing between atoms. Since interatomic interactions are minimal, the emitted radiation reflects the properties of individual atoms and produces characteristic line spectra. Therefore, option B is correct.

❓ Why Other Options Are Incorrect

�� Option A → Incorrect because rarefied gases produce line spectra, not continuous spectra.
�� Option C → Incorrect because each element has a unique spectrum.
�� Option D → Incorrect because glow tubes operate through electrical excitation, not alpha emission.

🎯 Strategy

Used

Elimination

Application:

Reject statements inconsistent with low-pressure gas behavior.

Final Logic:

Large atomic spacing leads to characteristic atomic spectra.

🧠 Memory Trick

Glow Tube = Line Spectrum

📚 Class XII – NCERT Physics Part II – Chapter: Atoms – Topic: Spectra of Rarefied Gases

11 The characteristic spectrum of an element and its utility in material analysis are described respectively as:

A Continuous, Heating

B Discrete, Fingerprint

C Continuous, Fingerprint

D Discrete, Heating

💡 Short Explanation

�� Each element emits specific wavelengths. �� Spectral lines are unique. �� Spectra help identify elements.

✅ Correct Answer Explanation

The spectrum of an element consists of discrete spectral lines corresponding to specific electronic transitions. Since every element has a unique arrangement of energy levels, its spectrum acts as a fingerprint for identification in chemical and astronomical analysis. Therefore, the correct answer is option B.

❓ Why Other Options Are Incorrect

�� Option A → Incorrect because elemental spectra are generally discrete rather than continuous.
�� Option C → Incorrect because characteristic spectra are not continuous.
�� Option D → Incorrect because heating is a method of excitation, not the analytical utility of the spectrum.

🎯 Strategy

Used

Contextual/Tonal Matching

Application:

Match the nature of elemental spectra with their practical application.

Final Logic:

Discrete spectral lines uniquely identify elements.

🧠 Memory Trick

Spectrum = Element Fingerprint

📚 Class XII – NCERT Physics Part II – Chapter: Atoms – Topic: Characteristic Spectra of Elements

12 Incorrect statement about the hydrogen spectrum:

A It consists of lines with fixed relative positions.

B The spacing between lines varies randomly with temperature.

C It suggested an intimate relationship with internal atomic structure.

D It was studied by Johann Jakob Balmer.

💡 Short Explanation

�� Hydrogen shows fixed spectral lines. �� Atomic structure determines wavelengths. �� Balmer studied hydrogen spectra.

✅ Correct Answer Explanation

Hydrogen spectral lines occur at definite wavelengths determined by electronic energy levels. Their positions do not vary randomly with temperature. The fixed pattern of lines led scientists to conclude that atomic structure governs radiation emission. Therefore, option B is correct.

❓ Why Other Options Are Incorrect

�� Option A → Correct because hydrogen lines occur at fixed relative positions.
�� Option C → Correct because hydrogen spectra revealed a connection with atomic structure.
�� Option D → Correct because Balmer formulated the empirical wavelength relation.

🎯 Strategy

Used

Odd One Out

Application:

Identify the statement contradicting the fixed nature of hydrogen spectral lines.

Final Logic:

Hydrogen spectral positions are fixed, not random.

🧠 Memory Trick

Hydrogen = Fixed Pattern

📚 Class XII – NCERT Physics Part II – Chapter: Atoms – Topic: Hydrogen Spectrum

13 Statements about spectral connections to atomic structure:
1. Discrete lines hint at quantized or restricted internal states.
2. Characteristic spectra serve as a fingerprint for elements.
3. The internal structure governs the specific wavelengths emitted.
4. Solids and rarefied gases emit the exact same spectral patterns.

A (1), (2), (3)

B (1), (3), (4)

C (2), (3), (4)

D (1), (2), (4)

💡 Short Explanation

�� Spectral lines arise from quantized states. �� Every element has a unique spectrum. �� Internal structure determines wavelengths.

✅ Correct Answer Explanation

Statement 1 is correct because discrete spectral lines indicate restricted energy states within atoms. Statement 2 is correct because characteristic spectra uniquely identify elements. Statement 3 is correct because atomic structure determines the emitted wavelengths. Statement 4 is incorrect because solids generally produce continuous spectra whereas rarefied gases produce line spectra. Therefore, statements 1, 2 and 3 are correct.

❓ Why Other Options Are Incorrect

�� Option B → Includes statement 4, which is incorrect.
�� Option C → Includes statement 4, which is incorrect.
�� Option D → Includes statement 4, which is incorrect.

🎯 Strategy

Used

Elimination

Application:

Evaluate each statement using spectral observations.

Final Logic:

Only statements 1, 2 and 3 agree with atomic spectroscopy.

🧠 Memory Trick

Lines → Levels → Structure

📚 Class XII – NCERT Physics Part II – Chapter: Atoms – Topic: Atomic Spectra and Atomic Structure

14 If the closest approach distance of an alpha particle depends on its initial kinetic energy, what is the maximum kinetic energy found in alpha particles of natural origin as stated in the Geiger-Marsden experiment analysis?

A 1.20 × 10⁻¹² J

B 1.05 × 10⁻¹² J

C 1.60 × 10⁻¹⁹ J

D 2.20 × 10⁻¹⁸ J

💡 Short Explanation

�� Alpha particles possess high kinetic energy. �� Closest approach depends on kinetic energy. �� Rutherford analysis used energetic alpha particles.

✅ Correct Answer Explanation

In Rutherford scattering analysis, the maximum kinetic energy of naturally occurring alpha particles is approximately 1.20 × 10⁻¹² J. This energy enables alpha particles to approach the nucleus closely before electrostatic repulsion brings them to rest momentarily. Therefore, option A is correct.

❓ Why Other Options Are Incorrect

�� Option B → Incorrect value not used in the standard analysis.
�� Option C → Incorrect because it is of the order of an electron volt rather than alpha-particle kinetic energy.
�� Option D → Incorrect because it exceeds the stated value.

🎯 Strategy

Used

Elimination

Application:

Compare the numerical values with the standard Rutherford scattering discussion.

Final Logic:

The accepted value is 1.20 × 10⁻¹² J.

🧠 Memory Trick

Alpha Energy ≈ 1.2 × 10⁻¹² J

📚 Class XII – NCERT Physics Part II – Chapter: Atoms – Topic: Distance of Closest Approach

15 The empirical formula obtained by Johann Jakob Balmer was significant because

A it explained the continuous radiation of condensed matter

B it provided a mathematical basis for the wavelengths of a group of lines emitted by atomic hydrogen

C it proved that atoms consist of a positive nucleus and orbiting electrons

D it demonstrated the wave nature of the electron

💡 Short Explanation

�� Balmer studied hydrogen lines. �� He derived a wavelength relation. �� The formula matched observations.

✅ Correct Answer Explanation

Balmer's empirical formula successfully described the wavelengths of visible spectral lines emitted by hydrogen. It was one of the earliest mathematical relationships in atomic spectroscopy and later became an important clue for atomic theory. Therefore, option B is correct.

❓ Why Other Options Are Incorrect

�� Option A → Incorrect because Balmer's formula applies to hydrogen line spectra.
�� Option C → Incorrect because Rutherford later proposed the nuclear model.
�� Option D → Incorrect because electron wave nature was introduced much later by de Broglie.

🎯 Strategy

Used

Contextual/Tonal Matching

Application:

Match Balmer's work with its actual scientific contribution.

Final Logic:

Balmer's formula explained hydrogen spectral wavelengths.

🧠 Memory Trick

Balmer = Hydrogen Formula

📚 Class XII – NCERT Physics Part II – Chapter: Atoms – Topic: Balmer Formula

16 Which of the following is correct regarding hydrogen's simplicity in early atomic theory?

A Its single electron made classical mechanics sufficient to explain its discrete emission.

B Its simplicity meant it only ever emitted a single wavelength of light.

C It was the only element whose atoms lacked a positive nucleus.

D Despite consisting of only one electron and proton, it emits a complex spectrum of specific wavelengths.

💡 Short Explanation

�� Hydrogen is the simplest atom. �� It still produces many spectral lines. �� Classical physics could not explain them fully.

✅ Correct Answer Explanation

Hydrogen contains only one proton and one electron, making it the simplest atom. Despite this simplicity, it emits many specific wavelengths arranged in spectral series, revealing the complexity of atomic energy levels. Therefore, option D is correct.

❓ Why Other Options Are Incorrect

�� Option A → Incorrect because classical mechanics failed to explain discrete spectra.
�� Option B → Incorrect because hydrogen emits many wavelengths, not just one.
�� Option C → Incorrect because hydrogen contains a positive nucleus.

🎯 Strategy

Used

Elimination

Application:

Remove statements inconsistent with hydrogen spectroscopy.

Final Logic:

The simplest atom still produces a rich line spectrum.

🧠 Memory Trick

Simple Atom, Complex Spectrum

📚 Class XII – NCERT Physics Part II – Chapter: Atoms – Topic: Hydrogen Atom

17 Incorrect statement about Rutherford's early radioactive research:

A He studied alpha particles emitted by elements like Bismuth-214.

B He collaborated with Frederick Soddy to create the modern theory of radioactivity.

C He discovered that alpha particles carry a negative charge.

D He discovered a new noble gas known as thoron.

💡 Short Explanation

�� Alpha particles are positively charged. �� Rutherford studied radioactivity extensively. �� He collaborated with Soddy.

✅ Correct Answer Explanation

Alpha particles are positively charged helium nuclei. Rutherford's studies established their positive nature. Therefore, the statement that alpha particles carry a negative charge is incorrect. Hence, option C is the correct answer.

❓ Why Other Options Are Incorrect

�� Option A → Correct statement regarding Rutherford's radioactivity studies.
�� Option B → Correct because Rutherford and Soddy developed the modern theory of radioactivity.
�� Option D → Correct because Rutherford identified thoron.

🎯 Strategy

Used

Odd One Out

Application:

Identify the statement contradicting known alpha-particle properties.

Final Logic:

Alpha particles are positively charged, not negatively charged.

🧠 Memory Trick

Alpha = Positive

📚 Class XII – NCERT Physics Part II – Chapter: Atoms – Topic: Rutherford and Radioactivity

18 The types of discrete rays discovered by Rutherford from radioactive elements are:

A Alpha, Gamma

B Alpha, Beta

C Beta, Gamma

D X-rays, Alpha

💡 Short Explanation

�� Rutherford identified alpha rays. �� He identified beta rays. �� These arose from radioactive substances.

✅ Correct Answer Explanation

Rutherford classified radioactive emissions into alpha and beta rays through experimental investigation. These discoveries played a major role in understanding radioactive decay and atomic structure. Therefore, option B is correct.

❓ Why Other Options Are Incorrect

�� Option A → Incorrect because gamma rays were identified later as electromagnetic radiation.
�� Option C → Incorrect because alpha rays were also discovered by Rutherford.
�� Option D → Incorrect because X-rays are not radioactive particles discovered by Rutherford.

🎯 Strategy

Used

Recall-Based Elimination

Application:

Associate Rutherford with the correct radioactive emissions.

Final Logic:

Rutherford identified alpha and beta radiations.

🧠 Memory Trick

Rutherford → Alpha + Beta

📚 Class XII – NCERT Physics Part II – Chapter: Atoms – Topic: Radioactive Radiations

19 Match List I with List II regarding foundational atomic concepts

List I	List II
1. Modern theory of radioactivity	a. J.J. Thomson
2. Plum pudding model	b. Rutherford and Soddy
3. Empirical hydrogen formula	c. Ernst Rutherford
4. Planetary model of atom	d. J.J. Balmer

A (1)-c, (2)-d, (3)-a, (4)-b

B (1)-a, (2)-b, (3)-c, (4)-d

C (1)-b, (2)-a, (3)-d, (4)-c

D (1)-b, (2)-d, (3)-a, (4)-c

💡 Short Explanation

�� Rutherford and Soddy developed radioactivity theory. �� Thomson proposed the plum pudding model. �� Balmer formulated the hydrogen equation. �� Rutherford proposed the planetary model.

✅ Correct Answer Explanation

1 → b : Modern theory of radioactivity → Rutherford and Soddy 2 → a : Plum pudding model → J.J. Thomson 3 → d : Empirical hydrogen formula → J.J. Balmer 4 → c : Planetary model of atom → Ernst Rutherford Thus, option C is correct.

❓ Why Other Options Are Incorrect

�� Option A → Multiple concepts matched with wrong scientists.
�� Option B → Multiple incorrect pairings.
�� Option D → Balmer is incorrectly associated with the plum pudding model.

🎯 Strategy

Used

Option Grouping

Application:

Match each scientific contribution with its contributor.

Final Logic:

Only option A correctly matches all four entries.

🧠 Memory Trick

Radioactivity-Soddy, Plum-Thomson, Formula-Balmer, Planetary-Rutherford

📚 Class XII – NCERT Physics Part II – Chapter: Atoms – Topic: Historical Development of Atomic Theory

20 Statements about thoron gas:
1. Discovered by Rutherford.
2. It is an isotope of radon.
3. It is considered a noble gas.
4. It is a fundamental constituent of all atoms.

A (1), (2), (3)

B (1), (3), (4)

C (2), (3), (4)

D (1), (2), (4)

💡 Short Explanation

�� Thoron is radioactive radon-220. �� It belongs to the noble gas family. �� It is not a constituent of all atoms.

✅ Correct Answer Explanation

Statement 1 is correct because Rutherford identified thoron during his studies of radioactive emanations. Statement 2 is correct because thoron is radon-220, an isotope of radon. Statement 3 is correct because radon belongs to the noble gases. Statement 4 is incorrect because thoron is a specific radioactive gas, not a universal constituent of matter. Therefore, statements 1, 2 and 3 are correct.

❓ Why Other Options Are Incorrect

�� Option B → Includes statement 4, which is incorrect.
�� Option C → Includes statement 4, which is incorrect.
�� Option D → Includes statement 4, which is incorrect.

🎯 Strategy

Used

Elimination

Application:

Check each statement against known properties of thoron.

Final Logic:

Only statements 1, 2 and 3 are correct.

🧠 Memory Trick

Thoron = Radon Noble Gas

📚 Class XII – NCERT Physics Part II – Chapter: Atoms – Topic: Rutherford's Radioactivity Studies

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