Consider the following statements regarding the physical and chemical properties of isotopes: 1. Isotopes of an element have different chemical properties. 2. Isotopes of an element have different physical properties. 3. The difference in mass numbers leads to differences in physical properties.

The correct option is (c). Explanation Isotopes are atoms of the same element that possess the same atomic number (number of protons) but different mass numbers (number of neutrons). The behavior of isotopes is categorized based on their electronic structure and nuclear mass. Statement-wise Analysis: - Statement 1 is Incorrect: Chemical properties are governed by the electronic configuration, specifically the number of valence electrons. Since isotopes of the same element have the same number of electrons and identical electronic configurations, they exhibit identical chemical properties. - Statement 2 is Correct: Physical properties such as density, boiling point, and melting point are influenced by the mass of the atom. Because isotopes differ in the number of neutrons, they have different atomic masses, which results in different physical properties. - Statement 3 is Correct: The variation in physical properties is directly attributed to the difference in mass numbers. For example, heavier isotopes generally have higher boiling points and densities compared to lighter isotopes of the same element. Key Takeaway: Isotopes of an element share identical chemical properties (due to the same electron count) but possess distinct physical properties (due to different nuclear masses).

NCERT Class 9 Science — Chapter 4: Structure of the atom

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Consider the following statements regarding the physical and chemical properties of isotopes:

Isotopes of an element have different chemical properties.
Isotopes of an element have different physical properties.
The difference in mass numbers leads to differences in physical properties.

Official previous-year question

Verified 1 Aug 2026.

Options

A1 and 2 only
B2 only
C2 and 3 only
D1, 2 and 3

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Solution

The correct option is (c).

Explanation

Isotopes are atoms of the same element that possess the same atomic number (number of protons) but different mass numbers (number of neutrons). The behavior of isotopes is categorized based on their electronic structure and nuclear mass.

Statement-wise Analysis:

Statement 1 is Incorrect: Chemical properties are governed by the electronic configuration, specifically the number of valence electrons. Since isotopes of the same element have the same number of electrons and identical electronic configurations, they exhibit identical chemical properties.
Statement 2 is Correct: Physical properties such as density, boiling point, and melting point are influenced by the mass of the atom. Because isotopes differ in the number of neutrons, they have different atomic masses, which results in different physical properties.
Statement 3 is Correct: The variation in physical properties is directly attributed to the difference in mass numbers. For example, heavier isotopes generally have higher boiling points and densities compared to lighter isotopes of the same element.

Key Takeaway:
Isotopes of an element share identical chemical properties (due to the same electron count) but possess distinct physical properties (due to different nuclear masses).

Your note

More from Chapter 4: Structure of the atom

Which sub-atomic particle was identified by J. Chadwick in 1932?

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With reference to Neils Bohr’s model of the atom, consider the following statements: 1. Only certain special orbits known as discrete orbits of electrons are allowed inside the atom. 2. Electrons radiate energy continuously while revolving in discrete orbits. 3. These discrete orbits are called energy levels. Which of the statements given above is/are correct?

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Consider the following statements regarding the discovery and properties of neutrons: 1. They were discovered by J.J. Thomson in 1897. 2. They are present in the nucleus of all atoms including hydrogen. 3. A neutron has no charge and a mass nearly equal to that of a proton. Which of the statements given above is/are correct?

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With reference to 'Valency', consider the following statements: 1. It is the combining capacity of the atoms of elements. 2. Atoms react to achieve a duplet in the outermost shell in all cases. 3. If the outermost shell has 8 electrons, the valency is 8. Which of the statements given above is/are correct?

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With reference to the definition of an element, consider the following statements: 1. Elements are defined by the number of protons they possess. 2. Atoms of a given element can have different numbers of protons. 3. The atomic number is characteristic of a particular element.

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The correct option is (c).

Explanation

Statement-wise Analysis:

Statement 1 is Incorrect: Chemical properties are governed by the electronic configuration, specifically the number of valence electrons. Since isotopes of the same element have the same number of electrons and identical electronic configurations, they exhibit identical chemical properties.
Statement 2 is Correct: Physical properties such as density, boiling point, and melting point are influenced by the mass of the atom. Because isotopes differ in the number of neutrons, they have different atomic masses, which results in different physical properties.
Statement 3 is Correct: The variation in physical properties is directly attributed to the difference in mass numbers. For example, heavier isotopes generally have higher boiling points and densities compared to lighter isotopes of the same element.

Key Takeaway:
Isotopes of an element share identical chemical properties (due to the same electron count) but possess distinct physical properties (due to different nuclear masses).