SEBA Class 9 Science Chapter 4 Structure of the Atom MCQs (2026–27) – Assam Eduverse
By Jamal Ali (M.Sc Physics, 5+ years teaching experience) · Reviewed by Editorial Board
Build a strong foundation in atomic structure with these SEBA Class 9 Science Chapter 4 Structure of the Atom MCQs (2026–27), carefully aligned with the latest ASSEB syllabus and current exam pattern. These SEBA Class 9 Science Chapter 4 Structure of the Atom MCQs feature a mix of conceptual and numerical questions that help students understand core topics while preparing effectively for board exams.
Curated by Assam Eduverse subject experts, these SEBA Class 9 Science Chapter 4 MCQs cover essential concepts such as subatomic particles, atomic models (Thomson, Rutherford, and Bohr), atomic and mass numbers, isotopes, and isobars. Solving these Structure of the Atom MCQs Class 9 SEBA and Assam Board Class 9 Science objective questions enhances accuracy and conceptual understanding. You can also practice more from Class 9 Science chapterwise MCQs and SEBA Class 9 MCQs.
Consistent revision of these ASSEB Class 9 Science Important MCQs will help you gain confidence and improve performance in exams. For detailed explanations, visit SEBA Class 9 Science Chapter 4 Structure of the Atom Solutions, or explore additional resources like SEBA Class 9 & 10 study materials and SEBA Class 9 syllabus.
SEBA Class 9 Science Chapter 4 Structure of the Atom MCQs – ASSEB 2026–27 Board Exam Practice
Table of Contents
Before You Start
Test your knowledge with the SEBA Class 9 Science MCQs Quiz. Read each question carefully and select the correct answer. Your answer is checked instantly after you choose an option, and a detailed explanation appears immediately to help you learn every concept and improve your exam preparation.
The stream of positively charged particles known as canal rays was discovered by which of the following physicists?
✅ Correct Answer
Concept Explanation
In 1886, German physicist Eugen Goldstein discovered a new type of radiation in a modified gas discharge tube containing a perforated cathode. He called these streams of positively charged subatomic rays "canal rays," which eventually led to the discovery of the proton.
Expressed in terms of standard electronic charge units, the relative electrical charge carried by a proton is:
✅ Correct Answer
Concept Explanation
A proton is a subatomic particle that carries a single unit of positive charge, denoted as +1. Its absolute charge value is equal in magnitude but opposite in sign to that of an electron, which carries a relative charge of -1.
In atomic mass calculations, the mass of a single proton is standardly taken to be approximately:
✅ Correct Answer
Concept Explanation
The relative mass of a proton is taken as 1 unit (approx. 1840 times heavier than an electron). Because an electron's mass is so small that it is considered negligible, the total mass of an atom depends entirely on the sum of its protons and neutrons.
According to the structural model proposed by J.J. Thomson, the negatively charged electrons are embedded inside a:
✅ Correct Answer
Concept Explanation
Thomson's classic "plum pudding" or "watermelon" model describes an atom as a uniform, positively charged sphere with negatively charged electrons embedded inside it like seeds or raisins to balance the charge.
Under Thomson's model configurations, why does an atom behave as an electrically neutral structure?
✅ Correct Answer
Concept Explanation
Even though Thomson's model lacked accuracy regarding internal structure, it successfully established that the absolute number of positive charges in the spherical body equals the absolute number of negative charges on the embedded electrons, rendering the atom electrically neutral overall.
During his alpha-particle scattering experiments, Ernest Rutherford selected a thin foil made of which metal?
✅ Correct Answer
Concept Explanation
Rutherford chose a **gold foil** because he needed an exceptionally thin layer to observe alpha particle deflections clearly. Gold is the most malleable metal, which allowed it to be hammered into a sheet only about 1000 atoms thick.
Rutherford observed that the vast majority of alpha particles traveled straight through the gold foil because:
✅ Correct Answer
Concept Explanation
Because nearly 99% of the fast-moving alpha particles shot straight through the target gold foil without experiencing any deflection or resistance, Rutherford concluded that the vast majority of an atom's total volume is comprised of empty space.
The small, dense, and positively charged structural center discovered at the heart of an atom is the:
✅ Correct Answer
Concept Explanation
Rutherford's scattering results demonstrated that the positive charge and nearly all the mass of an atom are concentrated in a tiny central region, which he discovered and named the nucleus.
How does the absolute physical size of a nucleus compare to the total size boundary of its host atom?
✅ Correct Answer
Concept Explanation
Rutherford calculated that the radius of the central nucleus is about 10⁵ times smaller than the total radius of the complete atom. To visualize this ratio, if an atom were scaled up to the size of a large sports stadium, the nucleus would be the size of a small marble placed at the center.
Which of the following scientists discovered the subatomic particle known as the neutron?
✅ Correct Answer
Concept Explanation
In 1932, British physicist James Chadwick discovered a new subatomic particle that carried no electrical charge but possessed a mass nearly equal to that of a proton. He named this neutral particle the neutron.
According to the Bohr-Bury electronic distribution rules, the maximum number of electrons that can reside inside the K-shell is:
✅ Correct Answer
Concept Explanation
The K-shell represents the first innermost energy level closest to the nucleus (n = 1). Applying the standard distribution capacity rule ($2n^2$), the maximum electron capacity is calculated as: $2 \times (1)^2 = 2$.
According to electron configuration constraints, the maximum number of electrons that can fit inside the L-shell is:
✅ Correct Answer
Concept Explanation
The L-shell represents the second energy level out from the nucleus (n = 2). Using the Bohr-Bury capacity formula ($2n^2$), the maximum number of electrons that this level can hold is: $2 \times (2)^2 = 2 \times 4 = 8$.
Which algebraic formula determines the maximum number of electrons that can be accommodated within a given energy shell 'n'?
✅ Correct Answer
Concept Explanation
The total electron capacity of any orbital energy shell depends on its principal shell index 'n'. The Bohr-Bury rule established that the capacity limit follows the expression 2n² (where n is the shell number 1, 2, 3, or 4 for shells K, L, M, or N).
Regardless of its principal index, the outermost valence shell of a stable atom can accommodate a maximum of:
✅ Correct Answer
Concept Explanation
According to the chemical octet rule rule of electron distribution, the outermost valence shell of any stable atom cannot hold more than 8 electrons, even if the shell has a larger theoretical capacity based on the $2n^2$ rule.
The chemical valency and bonding capacity of an element depends directly upon its:
✅ Correct Answer
Concept Explanation
Valency represents the combining power of an atom to achieve stability. It is determined entirely by the number of valence electrons (electrons in the outermost shell), which are either gained, lost, or shared during chemical bonding.
The fundamental atomic number (Z) of any element is defined as exactly equal to its total number of:
✅ Correct Answer
Concept Explanation
The atomic number ($Z$) defines the chemical identity of an element. It is equal to the total number of protons present inside the nucleus of an atom. While electron counts can change when ions form, the proton count remains constant for an element.
The total mass number (A) of a given atomic nucleus is computed by summing the number of:
✅ Correct Answer
Concept Explanation
The mass number ($A$) represents the total count of heavy subatomic particles located in the core. Because protons and neutrons reside in the nucleus, they are collectively termed nucleons, and their combined count determines the mass number.
Isotopes represent alternative structural variations of the same element that share the same:
✅ Correct Answer
Concept Explanation
Isotopes are atoms of the identical element that possess the matching atomic number (proton count) but hold different mass numbers because their nuclei contain a different number of neutrons. For example, Protium, Deuterium, and Tritium are all isotopes of hydrogen.
Isobars represent atoms of entirely different chemical elements that share the same:
✅ Correct Answer
Concept Explanation
Isobars are combinations of distinct elements that have different atomic numbers (meaning they have different counts of protons) but happen to share the identical total mass number because their total nucleon counts match. A classic example is Calcium (atomic number 20) and Argon (atomic number 18), which both share a mass number of 40.
Given that an Oxygen atom has an atomic number of 8, what is its stable chemical valency value?
✅ Correct Answer
Concept Explanation
With an atomic number of 8, oxygen has an electron configuration of (2, 6). Because its outer valence shell contains 6 electrons, it needs to gain 2 more electrons to reach a stable octet structure (8 electrons), which gives it a stable valency value of 2.
Assertion (A): The internal spatial framework of any given atom is composed mostly of completely empty space.
Reason (R): The vast majority of fast-moving alpha particles pass directly through a thin gold foil without suffering any spatial deflection.
✅ Correct Answer
Concept Explanation
During Rutherford's alpha-particle scattering experiment, the key observation was that almost all the high-energy alpha projectiles traveled straight through the metal target. This direct physical behavior serves as the experimental proof that confirms the assertion that atoms are mostly empty space inside.
Assertion (A): Neutrons carry an absolute net electrical charge value of zero.
Reason (R): Neutrons reside alongside protons inside the dense central core nucleus of the host atom.
✅ Correct Answer
Concept Explanation
Both statements are factually correct: neutrons are neutral subatomic particles with no electrical charge, and they reside inside the central nucleus. However, their location inside the nucleus does not explain why they lack an electrical charge, so the reason statement is not the correct explanation for the assertion.
Assertion (A): The atomic number parameter uniquely determines the chemical name and identity of any element.
Reason (R): The atomic number value corresponds exactly to the count of stable protons contained within the element's nucleus.
✅ Correct Answer
Concept Explanation
An element's identity depends on its proton count. Because the atomic number ($Z$) is defined as the number of protons in the nucleus, and because this value never changes during regular chemical reactions, it serves as the defining identifier for the element.
Assertion (A): Separate isotopes belonging to the same element display entirely different chemical properties.
Reason (R): All individual isotopes belonging to the same element share the exact same atomic number.
✅ Correct Answer
Concept Explanation
The assertion statement is false because isotopes actually display nearly identical chemical properties. Chemical properties are determined by an atom's electron configuration, and since all isotopes of an element share the same atomic number (as correctly noted in the reason statement), they share the same valence electron configuration and chemical reactivity.
Assertion (A): The chemical bonding valency value of elemental Neon gas is exactly zero.
Reason (R): Neon possesses a completely filled, stable outermost electronic valence shell configuration.
✅ Correct Answer
Concept Explanation
Neon holds an atomic number of 10, giving it an electron configuration of (2, 8). Because its outermost shell already contains the maximum limit of 8 electrons, it has a stable octet configuration and does not need to gain, lose, or share electrons, resulting in a valency of zero.
Assertion (A): According to structural postulates, the nuclear model proposed by Ernest Rutherford could not successfully account for the absolute electrodynamic stability of the atom.
Reason (R): Classical electromagnetic theory dictates that any accelerating, revolving electron would continuously lose energy via radiation and eventually spiral into the central nucleus.
✅ Correct Answer
Concept Explanation
Rutherford's planetary model described electrons orbiting a central positive nucleus. However, because circular motion involves continuous centripetal acceleration, classical electrodynamics states that charged particles must constantly radiate energy. Losing energy would cause the electron's orbit to shrink rapidly until it crashed into the nucleus, which would make atoms highly unstable. This major limitation was later resolved by Niels Bohr.
Match the foundational scientist in Column I with their primary structural contribution or breakthrough listed in Column II:
| Column I | Column II |
|---|---|
| (a) Ernest Rutherford | (i) Experimental discovery of the neutron |
| (b) J.J. Thomson | (ii) Postulation of the planetary nuclear model |
| (c) James Chadwick | (iii) Discovery of the negatively charged electron |
| (d) Eugen Goldstein | (iv) Discovery of positively charged canal rays |
✅ Correct Answer
Concept Explanation
Rutherford deduced the presence of a central atomic nucleus through alpha scattering, giving us the nuclear model. Thomson identified cathode rays as streams of electrons. Chadwick discovered the uncharged neutron in 1932, and Goldstein discovered canal rays in gas discharge tubes.
Which of the following characterizations are factually correct concerning the behavior and traits of physical isotopes? - (i) They maintain the exact same atomic number (Z)
- (ii) They possess completely different mass numbers (A)
- (iii) They display entirely distinct, non-identical chemical reactivities
- (iv) They exhibit virtually identical chemical properties due to matching electron configurations
✅ Correct Answer
Concept Explanation
Isotopes are variant atoms of the same element that share the same number of protons (same atomic number) but contain a different number of neutrons, which gives them different total mass numbers. Because chemical properties depend entirely on an atom's atomic number and outer valence electron configuration, isotopes exhibit identical chemical reactivities, which makes statement (iii) incorrect.
Assertion (A): Under standard calculation parameters, the maximum theoretical capacity of the M-shell is limited to exactly 18 electrons.
Reason (R): The maximum number of electrons that can occupy any principal quantum energy level is governed by the Bohr-Bury expression 2n².
✅ Correct Answer
Concept Explanation
The energy shells are indexed starting out from the nucleus as K (n=1), L (n=2), and M (n=3). Substituting the principal index n=3 into the standard Bohr-Bury allocation rule ($2n^2$) yields: $2 \times (3)^2 = 2 \times 9 = 18$. Therefore, the reason perfectly demonstrates why the assertion holds true.
Which of the following option entries cleanly represents the complete set of subatomic particles that make up an atom's structure? - (i) The proton
- (ii) The neutron
- (iii) The electron
- (iv) The core nucleus
✅ Correct Answer
Concept Explanation
An atom contains three fundamental **subatomic particles**: protons (positively charged), neutrons (electrically neutral), and electrons (negatively charged). The nucleus is not a particle itself; rather, it is the structural region at the center of the atom where protons and neutrons cluster together.
Match the structural shell terms in Column I with their corresponding electronic capacities or limits in Column II:
| Column I | Column II |
|---|---|
| (a) Innermost K-shell | (i) Holds a standard maximum capacity of 8 electrons |
| (b) Secondary L-shell | (ii) Holds a standard maximum capacity of 2 electrons |
| (c) Tertiary M-shell | (iii) Holds a standard maximum capacity of 18 electrons |
| (d) Outermost Valency shell | (iv) Strictly capped at a maximum limit of 8 electrons |
✅ Correct Answer
Concept Explanation
According to the Bohr-Bury electron distribution laws, the capacities of atomic shells progress using the formula $2n^2$, meaning K=2, L=8, and M=18. However, regardless of its theoretical index capacity, the chemical octet rule dictates that the outermost valence shell of any stable atom is always capped at a maximum of 8 electrons.
Assertion (A): Isobars represent atomic varieties that consistently display different atomic numbers.
Reason (R): By definition, any given set of isobars belongs to completely different chemical elements.
✅ Correct Answer
Concept Explanation
Isobars are atoms that share the same mass number but contain different atomic numbers. Because an element's chemical identity depends entirely on its atomic number (proton count), any atoms with different atomic numbers are automatically classified as different chemical elements. This explains why the assertion holds true.
Which of the following statements match the experimental parameters of Niels Bohr's atomic model? - (i) Orbiting electrons travel around the nucleus inside unique, discrete paths called orbits
- (ii) Electrons continually radiate energy outward while remaining inside these paths
- (iii) Only specific, non-continuous stable paths are permitted for orbital rotation
- (iv) Electrons do not lose or radiate energy as long as they stay within these allowed discrete orbits
✅ Correct Answer
Concept Explanation
Niels Bohr overcame the stability problems of Rutherford's model by introducing the concept of **discrete orbits** (or energy levels). He established that only certain specific paths are stable enough to allow electron rotation, and that while electrons remain within these stationary states, they do not radiate energy, which keeps the atom stable.
Assertion (A): The physical mass value of any given atom is concentrated almost entirely within its central nucleus.
Reason (R): Both heavy subatomic protons and neutrons are located inside the central core nucleus of the atom.
✅ Correct Answer
Concept Explanation
An atom contains three subatomic particles: protons, neutrons, and electrons. Protons and neutrons each possess a relative mass of 1 u, whereas an electron's mass is so small (1/1840 u) that it is considered negligible. Because the heavy protons and neutrons are located exclusively inside the nucleus, the entire atomic mass is concentrated right at the center.
Which of the following structural statements are factually correct regarding electrons? - (i) They carry a net negative charge magnitude
- (ii) They reside directly alongside protons inside the nucleus core
- (iii) Their relative mass contribution is negligible compared to a proton
- (iv) They are located in dynamic orbits spinning around the outer nucleus space
✅ Correct Answer
Concept Explanation
Electrons are negatively charged subatomic units that travel in orbits around the outside of the central nucleus, meaning statement (ii) is false. An electron's rest mass is tiny—approximately 1/1840th the mass of a proton—so its contribution to the overall mass of the atom is considered negligible.
Which of the following structural entries accurately describe the properties of isobars? - (i) They possess the identical atomic number (Z)
- (ii) They share the identical mass number (A)
- (iii) They possess completely different atomic numbers
- (iv) They belong by definition to entirely different chemical elements
✅ Correct Answer
Concept Explanation
Isobars are combinations of distinct elements that have completely different atomic numbers (proton counts) but happen to share the identical total mass number due to matching numbers of total nucleons. Because their atomic numbers differ, they automatically represent entirely different elements, which makes statement (i) incorrect.
Which of the following statement sets are accurate concerning atomic numbers and mass numbers? - (i) Atomic number corresponds to the total count of nuclear protons
- (ii) Mass number corresponds to the sum of protons and neutrons
- (iii) Atomic number corresponds to the sum of protons and neutrons
- (iv) Mass number is universally designated using the capital letter A
✅ Correct Answer
Concept Explanation
The atomic number ($Z$) tracks only the number of protons inside an atom's nucleus, which makes statement (iii) incorrect. The mass number ($A$) tracks the total number of heavy particles (protons + neutrons) inside the nucleus, and it is universally represented using the symbol **A**.
Match the particle or ray term in Column I with its appropriate electronic properties listed in Column II:
| Column I | Column II |
|---|---|
| (a) Isolated Electron | (i) Stream of positive particles tracking down gas channels |
| (b) Isolated Proton | (ii) Carries a negative charge magnitude of -1 unit |
| (c) Isolated Neutron | (iii) Carries a positive charge magnitude of +1 unit |
| (d) Canal Rays | (iv) Electrically neutral species carrying zero charge |
✅ Correct Answer
Concept Explanation
Electrons are the fundamental carrier particles of negative charge. Protons carry a +1 unit positive charge value, while neutrons carry no charge. Canal rays represent the streams of positive ions moving toward a cathode in gas discharge tubes.
Which of the following options correctly reflect the properties of chemical valency? - (i) Valency depends directly on the count of electrons in the outermost shell
- (ii) All noble gases carry an effective valency value of zero
- (iii) The element Oxygen possesses a stable valency value of 2
- (iv) The element Sodium possesses a stable valency value of 2
✅ Correct Answer
Concept Explanation
Valency is determined by the number of valence electrons an atom must gain, lose, or share to reach a stable state. Noble gases have completely filled outer shells, so their valency is zero. Oxygen (configuration 2, 6) needs to gain 2 electrons, giving it a valency of 2. Sodium holds an atomic number of 11 with a configuration of (2, 8, 1), meaning it loses 1 electron to become stable, so its valency is **1**, not 2.
Assertion (A): The element Chlorine exhibits a fractional relative atomic mass value calculated as 35.5 u.
Reason (R): Naturally occurring samples of Chlorine exist as a mixture of different isotopic forms in a fixed percentage ratio.
✅ Correct Answer
Concept Explanation
Natural chlorine exists as a mixture of two main isotopes: Chlorine-35 (approx. 75%) and Chlorine-37 (approx. 25%). Calculating the weighted average based on their relative abundance yields:
$(35 \times 75/100) + (37 \times 25/100) = 26.25 + 9.25 =$ **35.5 u**. This confirms that its fractional mass is a direct result of its isotopic composition.
Which of the following parameters are correct concerning the historic atomic model proposed by J.J. Thomson? - (i) The complete atom is structured as a uniform, positively charged sphere
- (ii) Negatively charged electrons are embedded inside this positive sphere
- (iii) The atom contains a dense central positive core region called a nucleus
- (iv) The complete atom remains electrically neutral overall
✅ Correct Answer
Concept Explanation
Thomson's model described the atom as a sphere of positive charge containing embedded electrons, which maintained net electrical neutrality. Statement (iii) is incorrect because the central **nucleus** was discovered later by Ernest Rutherford through his alpha particle scattering experiments.
Match the quantitative atomic terms in Column I with their definitions listed in Column II:
| Column I | Column II |
|---|---|
| (a) Atomic number (Z) | (i) The total count of nuclear protons and neutrons |
| (b) Mass number (A) | (ii) The total count of protons inside the nucleus |
| (c) Element Valency | (iii) The net structural combining capacity of an atom |
| (d) Nucleons | (iv) Collective term for particles inside the nucleus |
✅ Correct Answer
Concept Explanation
The atomic number tracks only the number of protons. The mass number sums protons and neutrons together. Valency defines an atom's combining power, and nucleons is the collective term for the protons and neutrons located inside the nucleus.
Match the distinct Hydrogen isotopes in Column I with their precise isotopic formula symbol designations in Column II:
| Column I | Column II |
|---|---|
| (a) Protium isotope | (i) ³₁H (Holds 1 proton and 2 neutrons) |
| (b) Deuterium isotope | (ii) ²₁H (Holds 1 proton and 1 neutron) |
| (c) Tritium isotope | (iii) ¹₁H (Holds 1 proton and 0 neutrons) |
| (d) Hydrogen isotopes general trait | (iv) All share an identical nuclear atomic number |
✅ Correct Answer
Concept Explanation
Protium is light hydrogen (¹₁H) containing zero neutrons. Deuterium is heavy hydrogen (²₁H) containing one neutron, and Tritium is the radioactive isotope (³₁H) containing two neutrons. Because they are all variants of the same element, they share the identical atomic number of 1.
Match the element in Column I with its appropriate chemical valency properties listed in Column II:
| Column I | Column II |
|---|---|
| (a) Inert Neon gas | (i) Possesses a stable combining valency value of 2 |
| (b) Oxygen gas element | (ii) Possesses an unreactive valency value of 0 |
| (c) Magnesium metal | (iii) Possesses a combining valency value of 1 |
| (d) Sodium metal element | (iv) Possesses a combining valency value of 2 |
✅ Correct Answer
Concept Explanation
Neon has a configuration of (2, 8), giving it a valency of 0. Oxygen has a configuration of (2, 6) and needs 2 electrons, giving it a valency of 2. Magnesium (2, 8, 2) readily loses 2 valence electrons, giving it a valency of 2, and Sodium (2, 8, 1) loses 1 valence electron, giving it a valency of 1.
Which of the following procedural rules are factually correct regarding electron distribution inside atoms? - (i) The maximum capacity limit for the innermost K-shell is 2
- (ii) The maximum capacity limit for the secondary L-shell is 8
- (iii) The outermost valence shell can hold a maximum of 8 electrons
- (iv) Energy shells are filled in a completely random spatial order
✅ Correct Answer
Concept Explanation
Bohr-Bury distribution rules require electron levels to be populated systematically in order of increasing energy. Electrons fill the inner shells first and progress outward in a stepwise fashion rather than randomly, which makes statement (iv) incorrect.
Match the materials in Column I with their nuclear or atomic property descriptions in Column II:
| Column I | Column II |
|---|---|
| (a) Isotope Systems | (i) Atoms that share an identical mass number value |
| (b) Isobar Systems | (ii) Variant atoms that share an identical atomic number value |
| (c) Chlorine-35 isotope | (iii) Contains exactly 17 protons inside its nucleus |
| (d) Carbon-14 isotope | (iv) Contains exactly 8 neutrons inside its nucleus |
✅ Correct Answer
Concept Explanation
Isotopes share the same atomic number. Isobars share the same mass number. Chlorine always has an atomic number of 17 (17 protons). Carbon-14 has a mass number of 14 and an atomic number of 6, meaning it contains: $14 - 6 =$ **8 neutrons**.
Match the scattering phenomena terms in Column I with their direct structural conclusions in Column II:
| Column I | Column II |
|---|---|
| (a) Alpha particle projectile | (i) A doubly charged Helium ion (He²⁺) |
| (b) Gold foil sheet target | (ii) Malleable metal sheet beaten down to a thin layer |
| (c) 180° structural deflection | (iii) Proves the existence of a small, dense nucleus |
| (d) Straight passage of most particles | (iv) Proves that the atomic volume is mostly empty space |
✅ Correct Answer
Concept Explanation
Alpha particles are fast-moving helium nuclei carrying a +2 charge. The gold foil acted as an ultra-thin atomic barrier. The rare 180° rebounds showed that a dense positive mass occupies a tiny fraction of the space, while the straight passage of most projectiles proved that the surrounding atomic space is mostly empty.
According to the observations from Rutherford's historic alpha-particle scattering experiment, which of the following conclusions were correct? - (i) The interior volume of an atom consists mostly of empty space
- (ii) The positive charge inside an atom occupies very little space
- (iii) Electrons reside stationary inside the central core nucleus
- (iv) Nearly all the mass of an atom is concentrated in the central nucleus
✅ Correct Answer
Concept Explanation
Rutherford concluded that an atom contains a tiny, dense, positively charged nucleus at its center that holds almost all its mass, and that the surrounding space is mostly empty. Statement (iii) is incorrect because Rutherford established that electrons move in orbits around the outside of the nucleus, rather than residing inside it.
Match the designation variables in Column I with their corresponding elemental parameters in Column II:
| Column I | Column II |
|---|---|
| (a) Atomic number notation | (i) Universally represented using the capital letter A |
| (b) Mass number notation | (ii) Universally represented using the capital letter Z |
| (c) Nitrogen structural formula | (iii) Standardly written as 7¹⁴N |
| (d) Carbon element structure | (iv) Contains exactly 6 protons inside its nucleus |
✅ Correct Answer
Concept Explanation
Atomic number is designated by Z, and mass number is designated by A. Nitrogen has an atomic number of 7 and a mass number of 14 (7¹⁴N). Carbon has an atomic number of 6, meaning it contains exactly 6 protons.
Match the stability or structural state in Column I with its appropriate chemical description in Column II:
| Column I | Column II |
|---|---|
| (a) Complete valence octet shell | (i) Tends to be chemically highly reactive to achieve stability |
| (b) Incomplete outer shell profile | (ii) Tends to be highly stable and chemically inert |
| (c) Bohr atomic model feature | (iii) Introduces discrete orbits to prevent energy radiation |
| (d) Rutherford model feature | (iv) Postulates that electrons revolve around a central nucleus |
✅ Correct Answer
Concept Explanation
An atom with a complete outer octet shell is stable and chemically inert. Atoms with incomplete outer configurations react readily to complete their shells. Bohr introduced discrete, stable orbits to keep atoms from collapsing, building upon Rutherford's discovery that electrons orbit a central positive nucleus.
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SEBA Class 9 Science Chapter 4 Structure of the Atom MCQs – Important Objective Questions
Understanding the Structure of the Atom is a key step in building a strong base in Chemistry. Regular practice of well-designed MCQs based on the latest SEBA (ASSEB) syllabus helps students develop clarity in fundamental concepts and become familiar with the pattern of objective questions asked in exams.
These SEBA Class 9 Science Chapter 4 MCQs cover essential topics such as atomic models, subatomic particles (electrons, protons, and neutrons), electronic configuration, valency, isotopes, and isobars. Since these concepts are directly linked to many higher-level topics, understanding them thoroughly is very important for long-term learning.
Practicing these important objective questions for Class 9 Science helps students improve their conceptual understanding and avoid confusion between similar terms and theories. It also strengthens their ability to answer questions related to atomic structure quickly and accurately in examinations.
Another advantage of consistent MCQ practice is better speed, accuracy, and confidence. Students become more comfortable with different question patterns, manage time efficiently, and can revise the entire chapter effectively before exams.
To perform well in school tests and board-level examinations, students should regularly solve such MCQs and focus on understanding the logic behind each answer. With consistent effort and smart revision, scoring high in this chapter becomes much easier and more achievable.
FAQs – SEBA Class 9 Science Chapter 4 Structure of the Atom MCQs
1. How many MCQs come from Structure of the Atom in SEBA Class 9 exam?
Around 4–6 MCQs usually come from this chapter out of the 45 total MCQs. Focus on atomic models and electrons for easy marks.
2. Which are the most important MCQs for Structure of the Atom Class 9 SEBA?
Questions on Bohr’s model, valency, and isotopes are most repeated. Practice previous papers to understand patterns quickly.
3. Is Structure of the Atom chapter difficult for SEBA Class 9 students?
No, it’s moderate if concepts are clear. Focus on diagrams and definitions—once basics are strong, MCQs become very easy.
4. Where can I download SEBA Class 9 Structure of the Atom MCQs with answers?
You can download chapter-wise MCQs with answers from Assam Eduverse. Always revise solved PDFs before exams for better accuracy.
5. How to prepare Structure of the Atom MCQs quickly before exam?
Revise key formulas, practice 20–30 MCQs daily, and focus on mistakes. Short revision notes help a lot during last-minute study.
6. Are previous year questions enough for Structure of the Atom MCQs SEBA?
Yes, many MCQs repeat with slight changes. Combine previous papers with Assam Eduverse practice sets for full exam preparation.
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