Choose the incorrect statement from the following:

Our Environment

Ozone Layer and How it is Getting Depleted

Options

(A)Ozone is a molecule formed by three atoms of oxygen.

(B)Ozone shields the surface of the Earth from ultraviolet radiations.

(C)Ozone is deadly poisonous.

(D)Ozone gets decomposed by UV radiations.

Official Answer

Ozone formationUV radiationmolecular oxygendeadly poisonstratosphere

Marking Scheme

11 Mark for correctly identifying Option D as the incorrect statement.

Hint

Think about how ozone is synthesized in the upper atmosphere. Does UV radiation act as the initiator for its formation or its decomposition?

Quick Oral Answer

Ozone is formed in the stratosphere when high-energy UV radiation splits molecular oxygen ( $O_2$ ) into free oxygen ( $O$ ) atoms. These free atoms are highly reactive and combine with existing $O_2$ molecules to form ozone ( $O_3$ ).

Analysis & Explanation

Based on the NCERT textbook, let us analyze each statement:

Statement A is correct (true): Ozone ( $O_3$ ) is indeed a molecule formed by three atoms of oxygen.
Statement B is correct (true): Ozone performs an essential function by shielding the surface of the Earth from harmful ultraviolet (UV) radiation from the Sun.
Statement C is correct (true): While essential at higher atmospheric levels, ozone is a deadly poison at the ground level.

Statement D is incorrect (false): UV radiation does not decompose ozone in the primary atmospheric cycle described; rather, high-energy UV radiation is responsible for the formation* of ozone. It splits molecular oxygen ( $O_2$ ) into free oxygen ( $O$ ) atoms, which then combine with molecular oxygen to form ozone as shown in the reactions:

$O_2 \xrightarrow{\text{UV}} O + O$

$O + O_2 \rightarrow O_3$

Therefore, the incorrect statement is D.

Common Mistakes

1Students often get confused and think UV radiation only destroys the ozone layer, forgetting that high-energy UV radiation is actually required to split molecular oxygen ( $O_2$ ) to form ozone ( $O_3$ ) in the first place.
2Confusing the toxic nature of ozone at ground level with its protective role in the stratosphere.

Interesting Facts

Although ozone is a deadly poison at ground level, it absorbs about 97-99% of the Sun's medium-frequency ultraviolet light, which otherwise would potentially damage highly sensitive biological systems on Earth.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2020?

This question carries 1 mark in the CBSE Class 10 Science 2020 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Our Environment" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Ozone Layer and How it is Getting Depleted" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2020 paper?

This is a MCQ question from Section A in the CBSE Class 10 Science 2020 paper.