Structure Of Atom MCQs Class 9 Topic Wise In Quiz Format

Here we are with “Structure of Atom MCQs” in quiz format. You can treat it as an online MCQ test.

The questions are created from the NCERT textbook of class 9 science chapter 4, Structure of Atoms.

How to get the best out of these MCQs? The answer is simple:

• Read your NCERT book thoroughly
• Prepare the important points from our short notes on the same chapter
• Practice again and again

The MCQS below are organised as :

1. First in plain MCQ format. You read the questions and options and see the correct answers
2. After the MCQ questions is the quiz section.

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Charged Particles in Matter

Q1. When two objects are rubbed together, they become charged mainly due to the transfer of:
A) Electrons
B) Protons
C) Neutrons
D) Entire atoms

✅ Answer: A

Explanation:
During rubbing, only electrons move from one body to another. Protons are tightly bound inside the nucleus and cannot move. Hence, charging occurs due to electron transfer.

Q2. The discovery that atoms are divisible first became clear after the identification of:
A) Proton
B) Neutron
C) Electron
D) Nucleus

✅ Answer: C

Explanation:
The discovery of the electron by J. J. Thomson proved that atoms contain smaller particles. Therefore, atoms are divisible.

Q3. Canal rays discovered by Goldstein were found to carry:
A) Negative charge
B) No charge
C) Mixed charge
D) Positive charge

✅ Answer: D

Explanation:
Canal rays consist of positively charged particles. They move in the opposite direction to cathode rays (electrons), showing they carry a positive charge.

Q4. The particle discovered from canal rays was later named:
A) Electron
B) Proton
C) Neutron
D) Positron

✅ Answer: B

Explanation:
Experiments on canal rays led to the discovery of the proton, a positively charged particle present in the nucleus.

Q5. The charge of a proton compared to an electron is:
A) Half
B) Double
C) Equal magnitude but opposite sign
D) Zero

✅ Answer: C

Explanation:
Electron charge = –1
Proton charge = +1
Both have equal magnitude but opposite signs, which balances the atom.

Q6. The mass of a proton is approximately how many times the mass of an electron?
A) 2000 times
B) 20 times
C) Equal
D) 1/2000 times

✅ Answer: A

Explanation:
A proton is about 2000 times heavier than an electron. Therefore, most atomic mass comes from protons (and neutrons), not electrons.

Q7. The symbol used to represent an electron is:
A) e⁻
B) p⁺
C) n⁰
D) e⁺

✅ Answer: A

Explanation:
Electron → e⁻
Proton → p⁺
Neutron → n⁰
The negative sign shows that the electron carries a negative charge.

Q8. Why can electrons be removed easily from an atom?
A) They are heavier
B) They are located outside the nucleus
C) They have no charge
D) They are tightly bound

✅ Answer: B

Explanation:
Electrons orbit the nucleus and are loosely bound. Protons are inside the nucleus and strongly bound, so only electrons can be easily removed.

Q9. Which particle is mainly responsible for the mass of an atom?
A) Electron
B) Photon
C) Neutron
D) Proton

✅ Answer: D

Explanation:
Electrons have negligible mass.
Protons (and neutrons) are heavy.
Since the proton mass ≈ is 1 unit, it contributes most to atomic mass.

Q10. The charge of an electron is considered:
A) +1
B) 0
C) +2
D) –1

✅ Answer: D

Explanation:
An electron carries one unit of negative charge (–1). This is the basic unit of negative electricity.

Q11. An atom remains electrically neutral because:
A) It has only neutrons
B) It has only protons
C) Total positive and negative charges balance
D) It contains no electrons

✅ Answer: A

Explanation:
This is a concept trap question.
Neutrality is not because of neutrons alone, but because:
number of protons = number of electrons → charges cancel.
Hence, the atom is overall neutral.

Q12. The scientist who discovered the electron was:
A) Goldstein
B) Rutherford
C) J.J. Thomson
D) Chadwick

✅ Answer: C

Explanation:
The electron was discovered using cathode ray experiments by J. J. Thomson in 1897.

Q13. Goldstein’s experiment used:
A) Alpha particles
B) Gas discharge tube
C) Magnetic field only
D) Sunlight

✅ Answer: B

Explanation:
Eugen Goldstein used a gas discharge tube and observed canal rays passing through holes in the cathode.

Q14. Canal rays move in a direction:
A) Opposite to cathode rays
B) Same as cathode rays
C) Randomly
D) Only sideways

✅ Answer: D

Explanation:
Canal rays pass through perforations in the cathode and appear to move sideways through the holes, unlike cathode rays, which move straight.

Q15. If an atom loses electrons, it becomes:
A) Positively charged
B) Negatively charged
C) Neutral
D) Radioactive

✅ Answer: A

Explanation:
Losing electrons means fewer negative charges.
Protons remain → more positive charge → atom becomes positively charged (cation).

Charged Particles in Matter Quiz

The Structure of an Atom

Thomson’s Model Of An Atom

Q1. According to the atomic model proposed by J. J. Thomson, electrons are located:
A) Outside the atom in fixed orbits
B) Inside the nucleus only
C) Embedded in a positively charged sphere
D) Moving randomly outside the atom

✅ Answer: C

Explanation:
Thomson suggested that the atom is a sphere of positive charge, and electrons are embedded inside it, like dry fruits inside a pudding. They are not orbiting outside or confined to a nucleus.

Q2. Thomson compared his atomic model to a Christmas pudding because:
A) The atom is hollow
B) Electrons are moving very fast
C) The atom is made only of electrons
D) Electrons are scattered like currants in pudding

✅ Answer: D

Explanation:
In a Christmas pudding, currants are spread throughout. Similarly, Thomson imagined electrons spread throughout a positive sphere, not concentrated in one place.

Q3. In Thomson’s model, the positive charge of the atom is:
A) Located only in the center
B) Present only on the surface
C) Absent
D) Spread uniformly throughout the atom

✅ Answer: D

Explanation:
Thomson proposed that the positive charge is uniformly distributed across the whole atom, forming a continuous sphere, with electrons embedded inside it.

Q4. Why is the atom electrically neutral in Thomson’s model?
A) Because it contains only neutrons
B) Because total positive charge equals total negative charge
C) Because electrons have no charge
D) Because a positive charge is absent

✅ Answer: B

Explanation:
Neutrality happens because the number of positive charges = the number of negative charges, so they cancel each other. Net charge becomes zero.

Q5. One major limitation of Thomson’s model was that it:
A) Could not explain the results of later experiments
B) Denied the existence of electrons
C) Said atoms are indivisible
D) Ignored positive charge completely

✅ Answer: A

Explanation:
Although the model explained neutrality, it failed to explain later experimental results (like scattering experiments). Hence, it was replaced by better atomic models.

Thomson’s Model Of An Atom Quiz

Rutherford’s Model Of An Atom

Q1. The scientist who performed the gold foil scattering experiment was:
A) J.J. Thomson
B) Chadwick
C) Bohr
D) Ernest Rutherford

✅ Answer: D

Explanation:
The experiment was conducted by Ernest Rutherford to study how particles are arranged inside the atom.

Q2. In Rutherford’s experiment, the particles used for bombardment were:
A) Electrons
B) Protons
C) Alpha particles
D) Neutrons

✅ Answer: C

Explanation:
Alpha particles (He²⁺ ions) were used because they are heavy and positively charged, so their deflection can reveal the internal structure of atoms.

Q3. Alpha particles carry a charge of:
A) +1
B) –1
C) 0
D) +2

✅ Answer: D

Explanation:
Alpha particles are helium ions with two protons and no electrons, so they carry a +2 charge.

Q4. Rutherford chose gold foil mainly because it:
A) Was highly reactive
B) Could be made extremely thin
C) Was cheap
D) Was very hard

✅ Answer: B

Explanation:
Gold is very malleable and can be beaten into extremely thin sheets, allowing particles to pass through easily.

Q5. The thickness of the gold foil was about:
A) 10 atoms
B) 100 atoms
C) 1000 atoms
D) 10,000 atoms

✅ Answer: C

Explanation:
The foil was about 1000 atoms thick, thin enough to observe scattering clearly.

Q6. Most alpha particles passed straight through the foil, showing that atoms are mostly:
A) Empty space
B) Positive
C) Negative
D) Solid

✅ Answer: A

Explanation:
Since most particles passed without deflection, there must be a large space inside the atom.

Q7. Small deflections of alpha particles indicate that:
A) Mass is evenly spread
B) Positive charge occupies little space
C) Electrons are heavy
D) The atom is solid

✅ Answer: B

Explanation:
Deflections occur when alpha particles come near the concentrated positive charge, which occupies only a small region.

Q8. A very small number of alpha particles rebounded because they:
A) Collided with electrons
B) Passed through space
C) Lost energy
D) Struck the dense nucleus

✅ Answer: D

Explanation:
Rebounding happens when alpha particles directly hit the dense, heavy nucleus, causing them to bounce back.

Q9. Roughly one out of every ______ alpha particles rebounded.
A) 100
B) 1000
C) 12,000
D) 1,00,000

✅ Answer: C

Explanation:
About 1 in 12,000 particles bounced back, showing the nucleus occupies very little space.

Q10. The central positively charged part of the atom is called the:
A) Orbit
B) Shell
C) Electron cloud
D) Nucleus

✅ Answer: D

Explanation:
Rutherford named the tiny, dense, positively charged centre the nucleus.

Q11. Nearly all the mass of an atom is concentrated in the:
A) Nucleus
B) Electron cloud
C) Orbits
D) Outer space

✅ Answer: A

Explanation:
Protons (and later neutrons) are located in the nucleus, so most of the atom’s mass is there.

Q12. In Rutherford’s model, electrons:
A) Are embedded in a positive charge
B) Remain fixed
C) Revolve around the nucleus
D) Stay inside the nucleus

✅ Answer: C

Explanation:
Electrons were proposed to revolve around the nucleus in circular orbits like planets around the Sun.

Q13. The size of the nucleus compared to the atom is:
A) Same
B) Much smaller
C) Slightly larger
D) Twice as large

✅ Answer: B

Explanation:
The nucleus is extremely tiny compared to the whole atom.

Q14. The radius of the nucleus is about ______ times less than the radius of the atom.
A) 10²
B) 10³
C) 10⁴
D) 10⁵

✅ Answer: D

Explanation:
The nucleus radius is about 10⁵ times smaller than the atomic radius.

Q15. Alpha particles are helium ions with a mass approximately:
A) 4 u
B) 1 u
C) 2 u
D) 8 u

✅ Answer: A

Explanation:
Alpha particles consist of 2 protons + 2 neutrons, giving a mass of about 4 atomic mass units (u).

Q16. If positive charge were spread throughout the atom, alpha particles would mostly:
A) Pass straight
B) Be strongly deflected
C) Be absorbed
D) Stop completely

✅ Answer: A

Explanation:
A uniform charge would cause only weak interactions, so particles would mostly pass through. Large deflections prove charge is concentrated.

Q17. Large angle deflections occur when alpha particles pass:
A) Far from the nucleus
B) Through empty space
C) Very close to the nucleus
D) Near electrons

✅ Answer: C

Explanation:
Strong repulsion happens only near the positively charged nucleus, causing sharp deflections.

Q18. Which statement is NOT explained by Rutherford’s model?
A) Presence of nucleus
B) Empty space in an atom
C) Stability of an atom
D) Scattering results

✅ Answer: C

Explanation:
The model failed to explain why electrons don’t lose energy and fall into the nucleus, so atomic stability was not explained.

Q19. According to physics, a revolving charged particle should:
A) Gain mass
B) Lose charge
C) Remain stable
D) Radiate energy

✅ Answer: D

Explanation:
Accelerated charges emit radiation. Hence, orbiting electrons should lose energy, which contradicts the stability of atoms.

Q20. If electrons lost energy continuously, they would eventually:
A) Move faster
B) Escape
C) Fall into the nucleus
D) Become neutral

✅ Answer: C

Explanation:
Loss of energy would shrink their orbit, causing electrons to spiral inward and collapse into the nucleus, making the atom unstable.

 Rutherford’s Model of the Atom

Bohr’s Model of the Atom

Q1. The atomic model that introduced fixed energy levels for electrons was proposed by:
A) Ernest Rutherford
B) James Chadwick
C) J.J. Thomson
D) Niels Bohr

✅ Answer: D

Explanation:
The concept of fixed energy shells was introduced by Niels Bohr, improving Rutherford’s model.

Q2. According to Bohr, electrons revolve only in:
A) Random paths
B) Elliptical paths
C) Discrete orbits
D) Straight lines

✅ Answer: C

Explanation:
Electrons are allowed only in certain fixed or discrete orbits, not anywhere between them. These are called energy levels.

Q3. The special orbits permitted for electrons are also called:
A) Waves
B) Clouds
C) Energy levels
D) Fields

✅ Answer: C

Explanation:
Each allowed orbit has definite energy, so these orbits are called energy levels or shells.

Q4. While moving in an allowed orbit, an electron:
A) Radiates energy continuously
B) Does not radiate energy
C) Gains a positive charge
D) Stops moving

✅ Answer: B

Explanation:
Bohr stated that electrons do not lose energy while revolving in fixed orbits. This explains atomic stability.

Q5. The first energy level closest to the nucleus is named:
A) L shell
B) M shell
C) K shell
D) N shell

✅ Answer: C

Explanation:
Shell naming starts from the inside outward:
K (n=1), L (n=2), M (n=3), N (n=4).
So the nearest shell is K.

Q6. The shell represented by quantum number n = 3 is called:
A) M shell
B) K shell
C) L shell
D) N shell

✅ Answer: A

Explanation:
Numbering rule:
n=1 → K
n=2 → L
n=3 → M
n=4 → N

Q7. Bohr’s model successfully explained the stability of atoms because electrons:
A) Are inside the nucleus
B) Continuously emit energy
C) Stay fixed without motion
D) Do not lose energy in allowed orbits

✅ Answer: D

Explanation:
Since electrons do not radiate energy in fixed orbits, they don’t spiral into the nucleus. Hence, atoms remain stable.

Q8. If an electron moves from one energy level to another, it will:
A) Remain unaffected
B) Become neutral
C) Change mass
D) Absorb or release energy

✅ Answer: D

Explanation:
Energy is exchanged only during transitions between shells. The electron absorbs energy to jump up and releases energy when it falls.

Bohr’s Model of the Atom Quiz

How are Electrons Distributed in Different Orbits (Shells)?

Q1. The rule for the distribution of electrons into different shells was proposed by:
A) Bohr and Bury
B) Rutherford only
C) Thomson only
D) Chadwick and Bohr

✅ Answer: A

Explanation:
The Niels Bohr – Charles Bury rules explain how electrons are arranged in different shells around the nucleus.

Q2. The maximum number of electrons in any shell is given by the formula:
A) n²
B) 8n
C) 2n
D) 2n²

✅ Answer: D

Explanation:
Maximum electrons = 2n², where n is the shell number.
This formula calculates the capacity of each energy level.

Q3. The maximum number of electrons that can be accommodated in the K-shell is:
A) 8
B) 4
C) 2
D) 18

✅ Answer: C

Explanation:
For K-shell, n = 1
2n² = 2 × 1² = 2 electrons

Q4. The L-shell can hold at most:
A) 2 electrons
B) 8 electrons
C) 18 electrons
D) 32 electrons

✅ Answer: B

Explanation:
For L-shell, n = 2
2n² = 2 × 2² = 2 × 4 = 8 electrons

Q5. The M-shell has a maximum capacity of:
A) 32 electrons
B) 8 electrons
C) 18 electrons
D) 16 electrons

✅ Answer: C

Explanation:
For M-shell, n = 3
2n² = 2 × 3² = 18
So it can hold 18 electrons.

Q6. According to shell filling rules, electrons first occupy the:
A) Outermost shell
B) Middle shell
C) Random shells
D) Innermost shell

✅ Answer: D

Explanation:
Electrons fill shells in a step-wise manner, starting from the shell closest to the nucleus (lowest energy).

Q7. The maximum number of electrons allowed in the outermost shell is:
A) 8
B) 18
C) 2
D) 32

✅ Answer: A

Explanation:
Regardless of capacity, the outermost shell cannot exceed 8 electrons. This is the octet rule for stability.

Q8. Which shell corresponds to n = 4?
A) M
B) L
C) K
D) N

✅ Answer: D

Explanation:
Shell naming sequence:
K → 1
L → 2
M → 3
N → 4

Q9. If a shell has not reached its maximum capacity, the next shell:
A) Fills simultaneously
B) Fills first
C) Remains empty
D) Starts filling immediately

✅ Answer: C

Explanation:
Electrons cannot enter the next shell until the inner shell is properly filled.

Q10. An atom with electronic configuration 2, 8, 8 follows which principle?
A) Random filling
B) Equal filling
C) Step-wise shell filling
D) Direct outer filling

✅ Answer: C

Explanation:
The arrangement shows inner shells filled first (2 → 8 → 8). This demonstrates the step-wise filling rule of electron distribution.

How are Electrons Distributed in Different Orbits (Shells)? Quiz

Valency

Q1. The electrons present in the outermost shell of an atom are called:
A) Valence electrons
B) Core electrons
C) Free electrons
D) Inner electrons

✅ Answer: A

Explanation:
Electrons in the outermost shell take part in chemical reactions. Hence, they are called valence electrons.

Q2. The maximum number of electrons that can be accommodated in the outermost shell is:
A) 2
B) 18
C) 8
D) 32

✅ Answer: C

Explanation:
According to the Bohr–Bury rule, the outermost shell can hold at most 8 electrons, giving stability (octet).

Q3. Atoms having completely filled outermost shells are generally:
A) Highly reactive
B) Positively charged
C) Unstable
D) Chemically inert

✅ Answer: D

Explanation:
When the outermost shell is full, atoms become stable and show very little chemical activity (like noble gases).

Q4. The combining capacity of an atom is known as its:
A) Atomic number
B) Mass number
C) Charge
D) Valency

✅ Answer: D

Explanation:
Valency is defined as the combining capacity of an atom or the number of electrons it gains, loses, or shares.

Q5. An outermost shell containing eight electrons is called an:
A) Pair
B) Duplet
C) Octet
D) Quartet

✅ Answer: C

Explanation:
Eight electrons in the outermost shell form an octet, which gives maximum stability.

Q6. Atoms achieve an octet by:
A) Sharing, gaining, or losing electrons
B) Increasing neutrons
C) Changing nucleus
D) Increasing mass

✅ Answer: A

Explanation:
Chemical reactions involve electron transfer or sharing, allowing atoms to complete their octet.

Q7. The valency of hydrogen is:
A) 0
B) 2
C) 1
D) 3

✅ Answer: C

Explanation:
Hydrogen has 1 valence electron and needs one more for stability (duplet), so its valency is 1.

Q8. The valency of sodium is:
A) 2
B) 1
C) 3
D) 0

✅ Answer: B

Explanation:
Sodium has one electron in the outermost shell and easily loses it → valency = 1.

Q9. Magnesium has two electrons in its outermost shell. Its valency is:
A) 1
B) 8
C) 3
D) 2

✅ Answer: D

Explanation:
Magnesium loses two electrons to get a stable configuration → valency = 2.

Q10. Aluminium contains three valence electrons. Therefore, its valency is:
A) 2
B) 1
C) 0
D) 3

✅ Answer: D

Explanation:
Aluminium loses three electrons to achieve stability → valency = 3.

Q11. The valency of an atom mainly depends on the number of:
A) Protons
B) Neutrons
C) Inner electrons
D) Valence electrons

✅ Answer: D

Explanation:
Only valence electrons participate in bonding, so they determine valency.

Q12. Fluorine has 7 electrons in its outermost shell. Its valency is:
A) 7
B) 2
C) 1
D) 0

✅ Answer: C

Explanation:
Instead of losing 7 electrons, fluorine gains 1 electron to complete its octet → valency = 1.

Q13. Oxygen has 6 valence electrons. Its valency will be:
A) 6
B) 4
C) 2
D) 8

✅ Answer: C

Explanation:
Octet − 6 = 2
Oxygen gains/shares 2 electrons → valency = 2.

Q14. An atom with valency zero will most likely belong to the group of:
A) Halogens
B) Alkali metals
C) Transition metals
D) Noble gases

✅ Answer: D

Explanation:
Atoms with full shells are noble gases, which show valency = 0 and are chemically inactive.

Q15. If an atom gains two electrons to complete its octet, its valency is:
A) 2
B) 6
C) 8
D) 1

✅ Answer: A

Explanation:
Valency equals the number of electrons gained, lost, or shared. Gaining two electrons means valency = 2.

Valency Quiz

Atomic Number

Q1. The atomic number of an element is equal to the number of:
A) Protons
B) Neutrons
C) Electrons only
D) Shells

✅ Answer: A

Explanation:
Atomic number is the total number of protons in the nucleus. Protons uniquely identify an element.

Q2. The symbol represents the atomic number:
A) A
B) M
C) Z
D) N

✅ Answer: C

Explanation:
Atomic number is denoted by Z, while mass number is usually denoted by A.

Q3. All atoms of the same element have the same number of:
A) Neutrons
B) Electrons
C) Shells
D) Protons

✅ Answer: D

Explanation:
Elements are defined by their proton count. Changing protons changes the element itself.

Q4. If an atom has an atomic number of 8, it must contain:
A) 8 neutrons
B) 8 protons
C) 8 shells
D) 16 electrons

✅ Answer: B

Explanation:
Atomic number directly gives the number of protons, so Z = 8 → 8 protons.

Q5. The element with atomic number 1 is:
A) Helium
B) Oxygen
C) Carbon
D) Hydrogen

✅ Answer: D

Explanation:
Hydrogen has one proton, so its atomic number is 1.

Q6. The element with atomic number 6 is:
A) Carbon
B) Nitrogen
C) Oxygen
D) Lithium

✅ Answer: A

Explanation:
Carbon has six protons, Z = 6.

Q7. In a neutral atom, the number of electrons is equal to the number of:
A) Neutrons
B) Shells
C) Protons
D) Orbits

✅ Answer: C

Explanation:
Positive charge of protons balances negative charge of electrons, so electrons = protons.

Q8. If the number of protons changes in an atom, the atom becomes a different:
A) Isotope
B) Ion
C) Molecule
D) Element

✅ Answer: D

Explanation:
Changing the proton number changes the atomic number, which means the identity of the element changes.

Q9. Which particle directly determines the identity of an element?
A) Electron
B) Neutron
C) Proton
D) Photon

✅ Answer: C

Explanation:
Only the proton number defines which element it is. Electrons or neutrons can change without changing identity.

Q10. An atom has 11 protons. Its atomic number will be:
A) 22
B) 1
C) 0
D) 11

✅ Answer: D

Explanation:
Atomic number = number of protons.
So, 11 protons → Z = 11.

Atomic Number Quiz

Mass Number

Q1. The mass of an atom is mainly due to the presence of:
A) Protons and neutrons
B) Electrons only
C) Protons only
D) Electrons and photons

✅ Answer: A

Explanation:
Electrons have negligible mass. Almost the entire mass comes from protons and neutrons, which are present inside the nucleus.

Q2. Protons and neutrons together are called:
A) Electrons
B) Positrons
C) Ions
D) Nucleons

✅ Answer: D

Explanation:
Since both particles are located in the nucleus, they are collectively called nucleons.

Q3. The mass number of an atom is the sum of:
A) Electrons + protons
B) Protons + neutrons
C) Neutrons + electrons
D) Shells + electrons

✅ Answer: B

Explanation:
Mass number counts only nucleons (protons + neutrons). Electrons are not included due to very small mass.

Q4. The symbol denotes the mass number:
A) Z
B) N
C) M
D) A

✅ Answer: D

Explanation:
Mass number is represented by A, while atomic number is represented by Z.

Q5. An atom has 8 protons and 8 neutrons. Its mass number is:
A) 8
B) 16
C) 10
D) 64

✅ Answer: B

Explanation:
Mass number = protons + neutrons
= 8 + 8 = 16

Q6. The mass of an atom resides mainly in the:
A) Shells
B) Electron cloud
C) Nucleus
D) Orbits

✅ Answer: C

Explanation:
The nucleus contains protons and neutrons, which contribute almost all the mass. Hence mass is concentrated in the nucleus.

Q7. The mass number of Carbon is 12 because it has:
A) 6 protons + 6 neutrons
B) 12 protons
C) 6 neutrons only
D) 12 electrons

✅ Answer: A

Explanation:
Carbon has 6 protons and 6 neutrons.
6 + 6 = 12 u, so mass number = 12.

Q8. The mass number of Aluminium is 27 because it contains:
A) 13 protons + 13 neutrons
B) 27 protons
C) 13 protons + 14 neutrons
D) 14 protons + 13 neutrons

✅ Answer: C

Explanation:
Aluminium has 13 protons and 14 neutrons.
13 + 14 = 27 u.

Q9. In the notation ¹⁴₇N, the number 14 represents the:
A) Atomic number
B) Electron number
C) Neutron number
D) Mass number

✅ Answer: D

Explanation:
In the symbol for Nitrogen, the top number (14) shows the mass number (A).

Q10. If an atom has a mass number of 23 and an atomic number of 11, the number of neutrons is:
A) 34
B) 23
C) 11
D) 12

✅ Answer: D

Explanation:
Neutrons = Mass number − Atomic number
= 23 − 11 = 12 neutrons.

Mass Number Quiz

Isotopes

Q1. Isotopes are atoms of the same element having the same:
A) Mass number
B) Number of neutrons
C) Atomic number
D) Physical properties

✅ Answer: C

Explanation:
Isotopes have the same number of protons (atomic number) but differ in the number of neutrons, giving different mass numbers.

Q2. Isotopes of an element differ in their:
A) Atomic number
B) Chemical properties
C) Number of protons
D) Mass number

✅ Answer: D

Explanation:
Since neutron numbers vary, the mass number changes, while the atomic number stays the same.

Q3. The three isotopes of Hydrogen are protium, deuterium, and:
A) Helium
B) Tritium
C) Positron
D) Neon

✅ Answer: B

Explanation:
Hydrogen has three isotopes:
Protium (¹H), Deuterium (²H), Tritium (³H).

Q4. Protium contains:
A) 1 proton and 2 neutrons
B) 1 proton and 1 neutron
C) Only 1 proton and no neutrons
D) 2 protons

✅ Answer: C

Explanation:
Protium (¹H) has 1 proton and 0 neutrons, making it the lightest isotope.

Q5. Chemical properties of isotopes are generally:
A) Completely different
B) Similar
C) Opposite
D) Random

✅ Answer: B

Explanation:
Chemical properties depend on electrons, and isotopes have the same number of electrons, so their chemical behavior is similar.

Q6. Physical properties of isotopes are different because they have different:
A) Charges
B) Atomic numbers
C) Electron numbers
D) Masses

✅ Answer: D

Explanation:
Physical properties like density and mass depend on mass, which differs among isotopes.

Q7. Chlorine occurs naturally mainly as isotopes of mass numbers:
A) 35 and 36
B) 35 and 37
C) 34 and 36
D) 37 and 39

✅ Answer: B

Explanation:
Chlorine exists as two isotopes: ³⁵Cl and ³⁷Cl.

Q8. The average atomic mass of chlorine is 35.5 u because:
A) Each atom weighs 35.5 u
B) Only one isotope exists
C) It is the weighted average of its isotopes
D) Neutrons have fractional mass

✅ Answer: C

Explanation:
Average atomic mass is calculated by considering the percentage abundance of each isotope, giving a weighted average.

Q9. An isotope of Uranium is commonly used as:
A) Fertilizer
B) Medicine for a cold
C) Food preservative
D) Fuel in nuclear reactors

✅ Answer: D

Explanation:
Uranium isotopes (like U-235) are used as nuclear fuel because they release large amounts of energy during fission.

Q10. An isotope of Cobalt is used mainly in:
A) Cooking
B) Cancer treatment
C) Lighting
D) Batteries

✅ Answer: B

Explanation:
Cobalt-60 emits gamma rays and is used in radiotherapy for cancer treatment.

Isotopes MCQ Quiz

Isobars

Q1. Isobars are atoms that have the same:
A) Atomic number
B) Number of electrons
C) Mass number
D) Chemical properties

✅ Answer: C

Explanation:
Isobars are defined as atoms of different elements that have the same mass number (A) but different atomic numbers.

Q2. Isobars belong to:
A) The same element
B) Different elements
C) The same isotope
D) The same molecule

✅ Answer: B

Explanation:
Since atomic numbers are different, isobars represent different elements, not the same one.

Q3. Two atoms are isobars if they have:
A) Same protons but different neutrons
B) Same neutrons but different protons
C) Same electrons and protons
D) Same total number of nucleons

✅ Answer: D

Explanation:
Mass number = protons + neutrons = nucleons.
Isobars have the same total nucleons, hence same mass number.

Q4. The atomic numbers of isobars are always:
A) Equal
B) Zero
C) Different
D) Multiple

✅ Answer: C

Explanation:
If atomic numbers were the same, they would be isotopes.
Since they are isobars, atomic numbers must differ.

Q5. Which of the following pairs is an example of isobars?
A) ¹₂H and ²₁H
B) ¹²₆C and ¹⁴₆C
C) ⁴⁰₂₀Ca and ⁴⁰₁₈Ar
D) ³⁵₁₇Cl and ³⁷₁₇Cl

✅ Answer: C

Explanation:
Calcium (Z=20) and Argon (Z=18) both have mass number 40, so they are isobars.

Q6. Isobars have different chemical properties because they have different numbers of:
A) Neutrons
B) Nucleons
C) Protons
D) Mass numbers

✅ Answer: C

Explanation:
Chemical properties depend on protons (atomic number). Since isobars have different protons, their properties differ.

Q7. The mass number of an isobar pair is:
A) Always different
B) Always the same
C) Zero
D) Half

✅ Answer: B

Explanation:
By definition, isobars share the same mass number.

Q8. If two atoms have mass number 56 but atomic numbers 26 and 25, they are:
A) Isotopes
B) Ions
C) Molecules
D) Isobars

✅ Answer: D

Explanation:
Same mass number (56) but different atomic numbers → they fit the definition of isobars.

Isobar MCQ Quiz