9th Std Science Solution in English | Lesson.11 Atomic Structure

Lesson 11 Atomic Structure

9th Science Guide Atomic Structure:  In this post, we will explore the book back answers for the lesson “Atomic Structure” from the 9th Standard Science curriculum. Understanding atomic structure is fundamental in the field of chemistry as it provides crucial insights into the composition and behavior of matter.

Atomic Structure Book Back Answer

Are you looking for answers to the book-back questions related to the Lesson Atomic Structure? Look no further! We have compiled the answers to help you test your knowledge and solidify your understanding of this important scientific concept.

I. Multiple-Choice Questions

1. Among the following the odd pair is

9th Science Guide Atomic Structure Answers in English a

Ans: c

2. Change in the number of neutrons in an atom changes it to

    1. an ion
    2. an isotope.
  1. an isobar
  2. another element.

Ans: an isotope

3. The term nucleons refers to

  1. Protons and electrons
  2. only Neutrons
  3. electrons and neutrons
  4. Protons and neutrons

Ans : Protons and neutrons

4. The number of protons, neutrons, and electrons present respectively in 9th Science Guide Atomic Structure Answers in English a are

  1. 80, 80, 35
  2. 35, 55, 80
  3. 35, 35, 80
  4. 35, 45, 35

Ans: 35, 45, 35

5. The correct electronic configuration of potassium is

  1. 2,8,9
  2. 2,8,1
  3. 2,8,8,1
  4. 2,8,8,3

Ans: 2,8,8,1

II. True or False if false give the correct answer:

1. In an atom, electrons revolve around the nucleus in fixed orbits.

Ans: True

2. Isotopes of an element have different atomic numbers.

Ans: False

Correct Ans: They have different mass numbers.

3. Electrons have negligible mass and charge.

Ans: True

4. Smaller the size of the orbit, the lower is the energy of the orbit.

Ans: True

5. The maximum number of electrons in L shell is 10.

Ans: False

Correct Ans: The maximum number of electrons in L shell is 8.

III. Fill in the Blanks

1. Calcium and Argon are examples of a pair of ________

Ans: Isobars

2. Total Number of electrons that can be accommodated in an orbit is given by ________

Ans: 2n2

3. _______ isotope is used in the treatment of goiter

Ans: Iodine -131

4. The number of neutrons present in is ________

Ans: 4

5. The valency of Argon is ________

Ans: Zero

IV. Match the following

1. DaltonHydrogen atom model
2. ThomsonPlanetary model
3. RutherfordFirst atomic theory
4. Neils BohrPlum pudding model
Discovery of neutrons
Ans ; 1 -C, 2 – D, 3 – B, 4 – A
1. Mass of proton1.6 X 10-19 C
2. Mass of electron-1.6 X 10-19 C
3. Charge of electron9.31 X 10-28 g
4. Charge of proton1.67 X 10-24 g
Ans ; : 1 – D, 2 – C, 3 – B, 4 – A

V. Complete the following table

Atomic NumberMass NumberNumber of NeutronsNumber of ProtonsNumber of ElectronsNumber of the Element

VI. Very short answer

1. Name an element which has the same number of electrons in its first and second shell.

Beryllium (2,2)

2. Write the electronic configuration of K+ and Cl

Electronic configuration of K+ is (2,8,8)

The electronic configuration of Cl is (2,8,8)

So, they are Iso-electronic

3. For an atom ‘X’, K, L, and M shells are completely filled. How many electrons will be present in it?

Total number of electrons= K + L +M
= 2+8+18=28

4. Compare the charge and mass of protons and electrons.

Proton1.602 x 10-19C 1.672 x 10-24g
Electron1.602 x 10-19C9.108 x 10-24g


5. Ca2+ has completely filled the outer shell. Justify your answer.

Ca has electronic configurations 2,8,8,2. After losing 2 c-s it becomes 2,8,2 (completely filled outer shell.
Ca -2e Ca2+

2,8,8,2 2,8,8 (completely filled)

VII. Short answer

1. State the law of multiple proportions?

When two elements A and B combine together to form more than one compound, then masses of A which separately combines with a fixed mass of B are in a simple ratio.

2. List the uses of isotopes?

  • Cobalt-60 isotope is used in the treatment of Cancer.
  • Uranium-235 acts as a fuel in nuclear reactors.

3. What is isotone? Give an example.

Atoms of different elements with

  • Different atomic numbers
  • Different mass numbers.
  • Same number of neurtrons.

4. Calculate the number of neutrons, protons, and electrons.

  • atomic number 3 and mass number 7
  • atomic number 92 and mass number 238

VIII. Arrange the following in increasing order of atomic number:

Calcium, Silicon, Boron, Magnesium, Oxygen, Helium, Neon, Sulphur, Fluorine and Sodium

Helium < Boron < Oxygen < Fluorine < Neon < Sodium < Magnesium < Silicon < Sulphur < Calcium

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I hope these 9th Science Atomic Structure Book Back Answers help you in your studies! Let me know if you have any further questions.

Last Updated: 2nd July 2023