Class 9 Science Test Paper Chapter Structure of Atom | CBSE Board | Detailed Solutions & Marking Scheme

-

 

VEDANT SKILL ASSESSMENT SERIES – ACADEMIC YEAR 2026–27

Class: 9
Subject: Chemistry
Chapter: Structure of Atom
Max Marks: 30
Time: 1 Hour

GENERAL INSTRUCTIONS

  1. Read all questions carefully before answering.
    • Misreading the question and then blaming the paper will not increase your marks.
  2. Show proper steps wherever required.
    • "Sir, answer toh yahi aana tha" is not an accepted mathematical method.
  3. Write neatly and clearly.
    • If your handwriting requires a decoder machine, checking may become an adventure.
  4. Manage your time wisely.
    • Spending 45 minutes on one question and calling the rest "optional" is not a strategy.
  5. If you do not know the answer, you may cry silently. Loud crying, emotional speeches, and negotiations for hints are strictly prohibited.

SECTION A (7 Marks)

Q1. [1 Mark]

An atom of an element has 13 electrons and 14 neutrons. Which of the following correctly represents the composition and identity of its nucleus?

A. 13 protons and 14 neutrons, representing Aluminium
B. 14 protons and 13 neutrons, representing Silicon
C. 13 protons and 27 neutrons, representing Aluminium
D. 14 protons and 14 neutrons, representing Carbon

Q2. [1 Mark]

While conducting the alpha-particle scattering experiment, Rutherford observed that a tiny fraction of alpha-particles rebounded back by 180°. This direct observation led to which major breakthrough?

A. Electrons revolve around the nucleus in fixed circular orbits.
B. The entire mass and positive charge are concentrated in a microscopic space inside the atom.
C. Neutrons exist inside the nucleus alongside protons to stabilize the atom.
D. The mass of an electron is completely negligible compared to a proton.

Q3. [1 Mark]

An ion M²⁺ contains 10 electrons and 12 neutrons. What is the correct atomic number and mass number of the neutral element M?

A. Atomic number = 10, Mass number = 22
B. Atomic number = 12, Mass number = 22
C. Atomic number = 12, Mass number = 24
D. Atomic number = 14, Mass number = 26

Q4. [1 Mark]

Which of the following statements is entirely correct regarding a pair of chemical species that are classified as isobars?

A. They exhibit identical chemical properties because they have the same number of protons.
B. They possess identical physical properties but have different total nucleon counts.
C. They have the same total number of nucleons but possess different numbers of protons.
D. They possess the same electronic configuration but differ completely in mass number.

Q5. [1 Mark]

A certain element X has an atomic number of 15. What will be the absolute valency of this element when it combines with hydrogen to form a stable hydride?

A. 5
B. 3
C. 2
D. 1

Directions for Q6 & Q7

Select the correct option from the standard choices below:

A. Both A and R are true, and R is the correct explanation of A.
B. Both A and R are true, but R is not the correct explanation of A.
C. A is true, but R is false.
D. A is false, but R is true.

Q6. [1 Mark]

Assertion (A): An atom is electrically neutral as a whole despite containing heavily charged subatomic particles.

Reason (R): The total number of positively charged protons present inside the nucleus is exactly equal to the total number of negatively charged electrons revolving outside the nucleus.

Q7. [1 Mark]

Assertion (A): The chemical properties of two isotopes, such as Protium (¹₁H) and Deuterium (²₁H), are completely identical.

Reason (R): Isotopes possess the exact same mass number due to an equal distribution of neutrons inside their respective nuclei.

SECTION B (8 Marks)

Q8. [2 Marks]

Naturally occurring chlorine is found in two isotopic forms with atomic masses of 35 u and 37 u, existing in a ratio of 3 : 1.

Calculate the average atomic mass of chlorine based on this natural abundance.

Q9. [2 Marks]

Write the electronic configuration and deduce the valency of the following:

(a) A neutral sulphur atom (Atomic number = 16)

(b) A magnesium ion (Mg²⁺), where atomic number of Mg = 12

Q10. [2 Marks]

J.J. Thomson's model of an atom is often compared to a Christmas pudding or a watermelon.

Briefly explain how Thomson visualized the distribution of positive and negative charges within this atomic model.

Q11. [2 Marks]

Medical practitioners frequently utilize specific isotopes of certain elements in specialized treatments.

Identify the isotopes used in the treatment/diagnosis of:

(a) Goitre (enlargement of the thyroid gland)

(b) Cancer therapy

SECTION C (6 Marks)

Q12. [3 Marks]

Compare the atomic models proposed by J.J. Thomson, Ernest Rutherford, and Niels Bohr on the basis of:

(a) Position and arrangement of electrons

(b) Distribution of positive charge

(c) Stability of the atom

Q13. Complete the missing entries in the formal academic data table given below: [3]

Atomic NumberMass NumberNumber of NeutronsNumber of ProtonsNumber of ElectronsName of the Species
919(a) _____(b) _____9(c) _____
(d) _____241212(e) _____(f) _____

SECTION D (5 Marks)

Q14. [5 Marks]

Answer the following:

(a) State the Bohr–Bury rules for the distribution of electrons into different shells. [2 Marks]

(b) Draw neat, labelled electronic structures of:

  • Sodium (Atomic number = 11)
  • Oxygen (Atomic number = 8)

[2 Marks]

(c) Why do noble gases like Helium and Neon have a valency of zero?

[1 Mark]

SECTION E (4 Marks) – CASE STUDY

Q15. [4 Marks]

Read the passage carefully and answer the questions.

In an advanced school laboratory workshop, students were exploring how elements achieve chemical stability. The facilitator explained that the combining capacity of an atom is determined by its valence electrons. Elements tend to attain a completely filled outermost shell (an octet, or a duplet in the case of Helium), which represents minimum energy.

Non-metals generally achieve this by gaining or sharing electrons, whereas reactive metals lose their outermost electrons to form positively charged cations.

A student studies three elements P, Q, and R, having atomic numbers 7, 11, and 18, respectively.

Answer the following:

(a) Write the electronic configuration of element P and state its valency. [1 Mark]

(b) Which element (P, Q, or R) will readily lose an electron to attain stability? Name the element. [1 Mark]

(c) Compare the chemical reactivity of elements P and R based on their electronic configurations. Give a scientific reason. [2 Marks]

VEDANT SKILL ASSESSMENT SERIES – ACADEMIC YEAR 2026–27

Class 9 – Chemistry

Chapter: Structure of Atom

SOLVED ANSWER KEY WITH MARKING SCHEME

Max Marks: 30

SECTION A (7 Marks)

Q1. [1 Mark]

Correct Answer: A

Marking Scheme:

  • Correct option A – 1 Mark

Q2. [1 Mark]

Correct Answer: B

Marking Scheme:

  • Correct option B – 1 Mark

Q3. [1 Mark]

Solution:

For M²⁺,

Electrons = 10

Neutral atom electrons = 10 + 2 = 12

Atomic Number = 12

Neutrons = 12

Mass Number = 12 + 12 = 24

Correct Answer: C

Marking Scheme:

  • Correct option C – 1 Mark

Q4. [1 Mark]

Correct Answer: C

Marking Scheme:

  • Correct option C – 1 Mark

Q5. [1 Mark]

Atomic Number = 15

Electronic configuration = 2, 8, 5

Valence electrons = 5

Valency = 8 − 5 = 3

Correct Answer: B

Marking Scheme:

  • Correct option B – 1 Mark

Q6. [1 Mark]

Assertion is True.

Reason is also True.

Reason correctly explains the assertion.

Correct Answer: A

Marking Scheme

  • Correct option A – 1 Mark

Q7. [1 Mark]

Assertion is True.

Reason is False because isotopes have the same atomic number but different mass numbers.

Correct Answer: C

Marking Scheme

  • Correct option C – 1 Mark

SECTION B (8 Marks)

Q8. [2 Marks]

Average atomic mass

= [(35 × 3) + (37 × 1)] / 4

= (105 + 37) / 4

= 142 / 4

= 35.5 u

Marking Scheme

  • Correct formula/substitution – 1 Mark
  • Correct calculation and answer (35.5 u) – 1 Mark

Q9. [2 Marks]

(a) Sulphur (Z = 16)

Electronic configuration = 2, 8, 6

Valency = 2

(b) Mg²⁺ (Z = 12)

Neutral Mg = 2, 8, 2

Mg²⁺ loses 2 electrons

Electronic configuration = 2, 8

Valency of Mg = 2

Marking Scheme

Each subpart

  • Electronic configuration – ½ Mark
  • Correct valency – ½ Mark

Total = 2 Marks

Q10. [2 Marks]

According to Thomson's atomic model,

  • The atom is a positively charged sphere.
  • Electrons are embedded throughout this sphere.
  • Positive and negative charges balance each other, making the atom electrically neutral.

Marking Scheme

  • Positive sphere mentioned – 1 Mark
  • Electrons embedded and atom neutral – 1 Mark

Q11. [2 Marks]

(a) Goitre → Iodine-131

(b) Cancer treatment → Cobalt-60

Marking Scheme

  • (a) Correct isotope – 1 Mark
  • (b) Correct isotope – 1 Mark

SECTION C (6 Marks)

Q12. [3 Marks]

BasisThomsonRutherfordBohr
ElectronsEmbedded in positive sphereRevolve around nucleusRevolve in fixed shells
Positive chargeSpread uniformlyConcentrated in nucleusConcentrated in nucleus
StabilityCould not explainCould not explainExplained stable atom

Marking Scheme

  • Position of electrons – 1 Mark
  • Positive charge – 1 Mark
  • Stability – 1 Mark

Q13. [3 Marks]

Completed Table

Atomic NumberMass NumberNumber of NeutronsNumber of ProtonsNumber of ElectronsName of the Species
9191099Fluorine (F)
1224121212Magnesium (Mg)

Answers

  • (a) 10
  • (b) 9
  • (c) Fluorine (F)
  • (d) 12
  • (e) 12
  • (f) Magnesium (Mg)

Marking Scheme (3 Marks)

  • (a), (b), (c) correct — 1.5 Marks (0.5 mark each)
  • (d), (e), (f) correct — 1.5 Marks (0.5 mark each)

Total = 3 Marks

SECTION D (5 Marks)

Q14

(a) Bohr–Bury Rules [2 Marks]

  1. Maximum number of electrons in a shell = 2n².
  2. The outermost shell can have a maximum of 8 electrons.
  3. The shell next to the outermost can have a maximum of 18 electrons.
  4. Electrons occupy shells from lower to higher energy levels.

Marking Scheme

Any four correct rules

  • ½ Mark each

Total = 2 Marks

(b) Electronic Structures [2 Marks]

Sodium (Z = 11)

Electronic configuration

2, 8, 1

(K = 2, L = 8, M = 1)

Oxygen (Z = 8)

Electronic configuration

2, 6

(K = 2, L = 6)

Marking Scheme

  • Sodium diagram/configuration – 1 Mark
  • Oxygen diagram/configuration – 1 Mark

(c) [1 Mark]

Noble gases have completely filled valence shells.

Hence, they neither gain, lose nor share electrons.

Therefore, their valency is zero.

Marking Scheme

  • Filled outermost shell with correct conclusion – 1 Mark

SECTION E (4 Marks)

Q15

(a) [1 Mark]

Element P

Atomic Number = 7

Electronic configuration = 2, 5

Valency = 3

Marking

  • Configuration – ½ Mark
  • Valency – ½ Mark

(b) [1 Mark]

Element Q

Atomic Number = 11

It is Sodium (Na).

It loses one electron to attain stability.

Marking

  • Q identified – ½ Mark
  • Sodium named – ½ Mark

(c) [2 Marks]

P (Nitrogen)

  • Configuration = 2,5
  • Reactive because it needs three electrons to complete its octet.

R (Argon)

  • Configuration = 2,8,8
  • Has a completely filled outermost shell.
  • Chemically inert and least reactive.

Marking Scheme

  • P explained – 1 Mark
  • R explained with reason – 1 Mark

TOTAL = 30 MARKS

Comments

Post a Comment

Popular posts from this blog

Class 10 English Test Paper Chapter 1 A letter to God and Poem 1 Fire and Ice , Dust of Snow | GSEB Board | Detailed Solutions & Marking Scheme

-
VEDANT CLASSES - A Pathway to Success... Date: ___________ Subject: English Marks:  30 Section A (14 Marks) 1. Discursive Passage (600–700 words) Passage: Success is often misunderstood as something that comes instantly or through luck. However, in reality, success is the result of continuous effort, discipline, and patience. Many people admire successful individuals but fail to recognize the years of struggle behind their achievements. It is important to understand that failure is not the opposite of success, but rather a part of it. In today’s fast-paced world, people want quick results. They tend to give up when things do not go their way. This attitude can prevent them from achieving their goals. Instead, one should learn from mistakes and keep moving forward. Every challenge offers an opportunity to grow stronger and wiser. Another key factor in success is self-belief. Without confidence, even the most talented individuals may fail to achieve their potential. Believing in on...
Read more

JEE Main Target Series: Class 11 PCM Mega Mock

-
Vedant Advanced Engineering/Medical Mock Test Portal Vedant Classes Exam Portal ⚠️ Important Exam Instructions Subjects: Physics, Chemistry, Mathematics. Format Per Subject: 25 Questions (20 MCQs + 5 Numerical Integers). Total Matrix Structure: 75 Total Questions. Time Limit: 180 minutes total. Auto-submits at 00:00. MCQ Marking Scheme (Q1 - Q20): +4.0 for Correct; -1 for Incorrect. Integer Marking Scheme (Q21 - Q25): +4.0 for Correct; -1 for Incorrect answers. Submission Warning: Leaving the tab or window will trigger instant automatic submission. Examinee Full Name Class / Standard Select your Class Class 9 Class 10 ...
Read more

Class 11 Chemistry Numerical Worksheet Chapter 1 Some basic concepts of chemistry | Detailed Solutions & Marking Scheme

-
 Got it — I’ve reframed all 30 questions into slightly more elaborated, competency-based, student-friendly format while keeping them numerical-focused and beginner level 👇 Vedant Classes – A Pathway to Success Class 11 Chemistry – Chapter 1: Some Basic Concepts of Chemistry 📄 Competency-Based Worksheet (30 Questions – Elaborated Version) 🧠 Section A: Basic Understanding (Q1–Q6) Q1. Calculate the molecular mass of carbon dioxide (CO₂) and sulphuric acid (H₂SO₄) using atomic masses (C = 12, O = 16, H = 1, S = 32). Q2. Determine the number of moles present in 44 g of CO₂. Also identify what this mass represents in terms of molar mass. Q3. Calculate the total number of molecules present in 18 g of water. Explain the steps involved. Q4. A sample contains 1 mole of methane (CH₄). Find the total number of atoms present in the sample. Q5. Calculate the total number of electrons present in one molecule of ammonia (NH₃). (Atomic numbers: N = 7, H = 1) Q6. Determine the number of ...
Read more