With reference to the ozone layer, consider the following statements: 1. Ozone absorbs ultraviolet radiation from the sun. 2. The breakdown of ozone into oxygen is a physical change. 3. Ozone is an allotrope of oxygen. Which of the statements given above is/are correct?

The correct option is (c). Explanation The ozone layer is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet radiation. Chemically, ozone is a molecule composed of three oxygen atoms ($O_3$), distinct from the diatomic oxygen ($O_2$) found in the lower atmosphere. Statement-wise Analysis: - Statement 1 is Correct: Ozone effectively absorbs ultraviolet (UV) radiation, specifically UV-B and UV-C bands, from the sun. This absorption process shields living organisms on Earth from the harmful effects of high-energy radiation. - Statement 2 is Incorrect: The breakdown of ozone ($O_3$) into oxygen ($O_2$) involves the breaking and formation of chemical bonds ($2O_3 \rightarrow 3O_2$). Since the chemical composition of the substance changes, this is a chemical change, not a physical change. A physical change would only involve a change in state (e.g., liquid to gas) without altering the molecular structure. - Statement 3 is Correct: Allotropy is the property of an element to exist in two or more different forms in the same physical state. Ozone ($O_3$) and dioxygen ($O_2$) are the two most common allotropes of the element oxygen. Key Takeaway: Ozone is a chemical allotrope of oxygen that undergoes chemical reactions to absorb UV radiation; its decomposition into oxygen is a chemical change involving bond rearrangement.

NCERT Class 7 Science — Chapter 2: Physical and chemical changes

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With reference to the ozone layer, consider the following statements:

Ozone absorbs ultraviolet radiation from the sun.
The breakdown of ozone into oxygen is a physical change.
Ozone is an allotrope of oxygen.

Which of the statements given above is/are correct?

Official previous-year question

Verified 1 Aug 2026.

Options

A1 and 2 only
B2 only
C1 and 3 only
D1, 2 and 3

Did you get this right?

Solution

The correct option is (c).

Explanation

The ozone layer is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet radiation. Chemically, ozone is a molecule composed of three oxygen atoms ($O_3$), distinct from the diatomic oxygen ($O_2$) found in the lower atmosphere.

Statement-wise Analysis:

Statement 1 is Correct: Ozone effectively absorbs ultraviolet (UV) radiation, specifically UV-B and UV-C bands, from the sun. This absorption process shields living organisms on Earth from the harmful effects of high-energy radiation.
Statement 2 is Incorrect: The breakdown of ozone ($O_3$) into oxygen ($O_2$) involves the breaking and formation of chemical bonds ($2O_3 \rightarrow 3O_2$). Since the chemical composition of the substance changes, this is a chemical change, not a physical change. A physical change would only involve a change in state (e.g., liquid to gas) without altering the molecular structure.
Statement 3 is Correct: Allotropy is the property of an element to exist in two or more different forms in the same physical state. Ozone ($O_3$) and dioxygen ($O_2$) are the two most common allotropes of the element oxygen.

Key Takeaway:
Ozone is a chemical allotrope of oxygen that undergoes chemical reactions to absorb UV radiation; its decomposition into oxygen is a chemical change involving bond rearrangement.

Your note

More from Chapter 2: Physical and chemical changes

With reference to the burning of a magnesium ribbon, consider the following statements: 1. It burns with a dull blue flame. 2. The ash formed is chemically different from the magnesium ribbon. 3. The reaction produces a new substance called magnesium oxide. Which of the statements given above is/are correct?

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When the ash obtained from burning magnesium is dissolved in water, the resulting solution is:

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With reference to the reaction between Copper Sulphate and Iron, consider the following statements: 1. The colour of the solution changes from blue to green. 2. The green colour is due to the formation of Copper Oxide. 3. A brown deposit forms on the iron object, which is Rust (Iron Oxide). Which of the statements given above is/are correct?

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Which of the following pairs is correctly matched regarding the reaction of Copper Sulphate with Iron?

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With reference to the "Lime Water Test", consider the following statements: 1. It is a standard test for Carbon Dioxide gas. 2. The milky appearance is due to the formation of Calcium Oxide. 3. The chemical name of lime water is Calcium Hydroxide. Which of the statements given above is/are correct?

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The correct option is (c).

Explanation

Statement-wise Analysis:

Statement 1 is Correct: Ozone effectively absorbs ultraviolet (UV) radiation, specifically UV-B and UV-C bands, from the sun. This absorption process shields living organisms on Earth from the harmful effects of high-energy radiation.
Statement 2 is Incorrect: The breakdown of ozone ($O_3$) into oxygen ($O_2$) involves the breaking and formation of chemical bonds ($2O_3 \rightarrow 3O_2$). Since the chemical composition of the substance changes, this is a chemical change, not a physical change. A physical change would only involve a change in state (e.g., liquid to gas) without altering the molecular structure.
Statement 3 is Correct: Allotropy is the property of an element to exist in two or more different forms in the same physical state. Ozone ($O_3$) and dioxygen ($O_2$) are the two most common allotropes of the element oxygen.

Key Takeaway:
Ozone is a chemical allotrope of oxygen that undergoes chemical reactions to absorb UV radiation; its decomposition into oxygen is a chemical change involving bond rearrangement.