Science
CBSE
Science — CBSE Class X Sample Paper (2026-27)
Sample paper · 2026-27
Section A · Section B · Section C
This MCQ module is based on: Ozone Layer Depletion and Waste Management
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Ozone Layer Depletion and Waste Management
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13.4 The Ozone Layer — A Shield in the Sky
About 15–35 km above the ground, in a part of the atmosphere called the stratosphere, lies a thin layer of a pale-blue gas — ozone (O3). Although it is chemically the same element as the O2 we breathe, this extra atom makes all the difference — ozone absorbs almost all of the Sun's dangerous ultraviolet (UV) radiation.
13.4.1 How Ozone Forms
High-energy UV rays from the Sun split an ordinary oxygen molecule into two oxygen atoms. Each free atom then combines with another O2 molecule to give O3:
Formation of ozone:
\[ \text{O}_2 \xrightarrow{\text{UV}} \text{O} + \text{O} \]
\[ \text{O} + \text{O}_2 \longrightarrow \text{O}_3 \]
The same UV rays that make ozone are the ones ozone later absorbs — a self-regulating system that protects us.
13.4.2 Ozone Depletion — The CFC Story
Until the 1970s scientists assumed the ozone layer was permanent. In 1985, measurements over Antarctica revealed a large thinning — the famous "ozone hole". The culprit was found to be chlorofluorocarbons (CFCs), used widely in refrigerators, air-conditioners and aerosol sprays.
In the upper atmosphere, UV rays break CFCs apart, releasing highly reactive chlorine atoms. Each chlorine atom catalytically destroys ozone:
Simplified destruction reactions:
\[ \text{CFCl}_3 \xrightarrow{\text{UV}} \text{Cl}^\bullet + \text{other products}\]
\[ \text{Cl}^\bullet + \text{O}_3 \longrightarrow \text{ClO}^\bullet + \text{O}_2 \]
\[ \text{ClO}^\bullet + \text{O} \longrightarrow \text{Cl}^\bullet + \text{O}_2 \]
The chlorine atom emerges unchanged and attacks another ozone — a single Cl can destroy thousands of O3 molecules.
13.4.3 Effects of Ozone Depletion
- Skin cancer and severe sunburn due to extra UV-B on skin.
- Cataracts — clouding of the eye lens — leading to blindness.
- Weakening of the human immune system.
- Reduced rate of plant photosynthesis and lower crop yields.
- Damage to phytoplankton — the base of oceanic food webs.
13.4.4 Montreal Protocol (1987)
Montreal Protocol: an international agreement signed in September 1987 by which countries pledged to freeze and then phase out the production of CFCs. Thanks to the Protocol, ozone-depleting substances have fallen dramatically and scientists expect the ozone layer to fully recover by around 2066. It is widely seen as the most successful environmental treaty of the 20th century. India has banned CFC production since 2010.
13.5 Managing the Garbage We Make
Every household generates waste daily — peels, wrappers, broken toys, old batteries. What happens to it afterwards depends on whether nature can digest it or not.
13.5.1 Biodegradable vs Non-Biodegradable
| Property | Biodegradable | Non-biodegradable |
|---|---|---|
| Broken down by microbes? | Yes, in days to months | No (or only in hundreds of years) |
| Examples | Food scraps, paper, cotton, jute, leaves, animal dung, wood | Plastics, polythene bags, metals, glass, aluminium cans, DDT |
| Fate in environment | Recycled as nutrients by decomposers | Pile up, pollute soil & water, block drains |
| Harm | Smell & breeding of flies if left uncollected | Enter food chains, cause biomagnification |
Key idea: Biodegradable substances re-enter nature's cycles; non-biodegradable substances do not. Mixing the two makes recycling almost impossible.
13.5.2 Segregation at the Source
Separating waste the moment it is generated is the single most important habit. The Indian Government's Swachh Bharat Mission uses a three-bin system:
GREEN bin
Wet / biodegradable — kitchen & garden waste → compost
Wet / biodegradable — kitchen & garden waste → compost
BLUE bin
Dry / recyclable — paper, plastic, metal, glass → recycling
Dry / recyclable — paper, plastic, metal, glass → recycling
BLACK/RED bin
Hazardous — batteries, e-waste, syringes, sanitary pads → special units
Hazardous — batteries, e-waste, syringes, sanitary pads → special units
13.5.3 The 3 R's of Waste Management
ReduceCut down what we buy & throw: refuse single-use plastic, take cloth bags, switch off idle lights.
ReuseGive items a second life: refilling bottles, using old notebooks for rough work, cloth scraps as dusters.
RecycleProcess used items into new ones: paper → newsprint, PET bottles → fibre, scrap iron → rods.
13.5.4 Methods of Disposal
- Composting — kitchen and garden waste is piled in a pit; decomposers turn it into nutrient-rich manure in about 3 months.
- Vermicomposting — earthworms speed up composting, giving high-quality manure.
- Recycling — paper is shredded, pulped and rolled into new sheets; plastic is melted into pellets and remoulded.
- Incineration — burning hazardous waste at very high temperatures in closed furnaces (hospital waste).
- Sanitary landfills — lined pits where mixed rubbish is buried and covered daily.
- Sewage treatment — removes biological oxygen-demanding waste from water before release.
Activity 13.2 — Segregate Your Home Waste
L3 ApplyTake one day's garbage from your house and sort it into three heaps on old newspaper:
- Wet (peels, leftovers, egg-shells)
- Dry-recyclable (paper, plastic bottles, aluminium foil)
- Hazardous (old battery, medicine strip, compact-fluorescent bulb)
Predict: Which heap is the largest by weight? Which should never go to a normal landfill? Why?
In most Indian homes the wet heap is the largest (50–60 %) — this can all be composted at home. The hazardous heap is the smallest but the most dangerous: batteries contain mercury, lead & cadmium; CFL bulbs contain mercury vapour — if thrown with ordinary rubbish, these poisons leak into soil and groundwater. They must go to recognised collection centres.
Competency-Based Questions
In October 1985 British scientists reported a sudden thinning of the ozone layer over Antarctica. Within two years the world's governments met in Canada and signed a landmark treaty. By 2020 the ozone hole was clearly shrinking.
Q1. Name the treaty and the year it was signed. L1 Remember
Montreal Protocol, signed in 1987.
Q2. (MCQ) Which of the following is a major ozone-depleting substance? L1 Remember
(c) CFCs — their Cl atoms break ozone molecules in the stratosphere.
Q3. Why does a banana peel disappear in a few weeks in a compost pit but a plastic wrapper remain for centuries? L2 Understand
The banana peel is biodegradable — it is made of natural polymers (cellulose, starch) that enzymes of fungi and bacteria can break down. Plastic is a synthetic polymer with bonds that no micro-organism possesses the enzyme to cut, so it is non-biodegradable.
Q4. (Short answer) Give any two effects on humans of increased UV reaching the ground. L2 Understand
(i) Skin cancer; (ii) Cataracts in the eyes; (iii) Weakening of the immune system — any two.
Q5. (True / False + justify) Burying a polythene bag in the garden is a safe way to dispose of it. L4 Analyse
False. Polythene is non-biodegradable and will remain in the soil for hundreds of years. It blocks aeration, stops rainwater from percolating, and slowly leaches toxic micro-plastics that enter the food chain. The bag must be cleaned and given for recycling instead.
Assertion–Reason Questions
Options: (A) Both A & R true, R correctly explains A. (B) Both A & R true, R does NOT explain A. (C) A true, R false. (D) A false, R true.
Assertion (A): Ozone is useful in the stratosphere but harmful at ground level.
Reason (R): Ozone is a strong oxidising agent and damages lungs when inhaled.
(B) — Both statements are true, but R only explains the ground-level harm; it does not explain why stratospheric ozone is useful. So R does not fully explain A.
Assertion (A): Wet and dry waste must be collected in the same bin.
Reason (R): Mixed waste makes recycling and composting easier.
(D) — Both statements are false in their usual form; in fact wet and dry waste should be separated and mixing actually makes recycling harder.
Assertion (A): The Montreal Protocol phased out the production of CFCs.
Reason (R): CFCs release chlorine atoms that destroy stratospheric ozone.
(A) — Both true and R correctly explains A.
Frequently Asked Questions — Ozone Layer & Waste Management
What is ozone layer & waste management in Class 10 Science (CBSE board)?
Ozone Layer & Waste Management is a key topic in NCERT Class 10 Science Chapter 13 — Our Environment. It explains role of the ozone layer, ozone depletion, and biodegradable vs non-biodegradable waste management. Core ideas covered include ozone layer, UV radiation, CFC, Montreal Protocol. Mastering this subtopic is essential for scoring well in the CBSE Class 10 Science board exam because board papers repeatedly test these concepts through MCQs, short answers and long-answer questions. This part gives a complete, exam-ready explanation with activities, diagrams and competency-based practice aligned to NCERT.
Why is ozone layer important in NCERT Class 10 Science?
Ozone layer is important in NCERT Class 10 Science because it forms the foundation for understanding ozone layer & waste management in Chapter 13 — Our Environment. Without a clear idea of ozone layer, students cannot answer higher-order CBSE board questions involving UV radiation, CFC, Montreal Protocol. Board papers regularly include 2-mark and 3-mark questions on this concept, and competency-based questions often link ozone layer to real-life situations. Building clarity here pays off directly in board marks.
How is ozone layer & waste management tested in the Class 10 Science CBSE board exam?
The CBSE Class 10 Science board exam tests ozone layer & waste management through a mix of 1-mark MCQs, 2-mark short answers, 3-mark explanations with examples, 5-mark descriptive questions (often with diagrams or balanced equations) and 4-mark competency-based questions. Expect direct questions on ozone layer, UV radiation, CFC and application-based questions drawn from NCERT activities. Students who follow NCERT thoroughly and practice this chapter's questions consistently score in the 90%+ range.
What are the key terms to remember for ozone layer & waste management in Class 10 Science?
The key terms to remember for ozone layer & waste management in NCERT Class 10 Science Chapter 13 are: ozone layer, UV radiation, CFC, Montreal Protocol, biodegradable waste, non-biodegradable waste. Each of these concepts carries exam weightage and regularly appears in the CBSE board paper. Write clear one-line definitions of every term in your revision notes and revisit them before the exam. Linking these terms visually through a flowchart or concept map makes recall easier during the Class 10 Science board exam.
Is Ozone Layer & Waste Management included in the Class 10 Science syllabus for 2025–26 CBSE board exam?
Yes, Ozone Layer & Waste Management is a part of the NCERT Class 10 Science syllabus (2025–26) prescribed by CBSE. It falls under Chapter 13 — Our Environment — and is examined in the annual board paper. The current syllabus retains the full treatment of ozone layer, UV radiation, CFC as per the NCERT textbook. Because CBSE bases every board question on NCERT, studying this part thoroughly ensures complete syllabus coverage and guarantees marks from this chapter.
How should I prepare ozone layer & waste management for the CBSE Class 10 Science board exam?
Prepare ozone layer & waste management for the CBSE Class 10 Science board exam in three steps. First, read this NCERT part carefully, highlighting definitions and diagrams of ozone layer, UV radiation, CFC. Second, solve every in-text question and end-of-chapter exercise — CBSE questions often come directly from NCERT. Third, practice competency-based and assertion-reason questions to sharpen reasoning. Write answers in the exam-style format (point-wise with diagrams) and time yourself. This method delivers confidence and full marks in the board exam.
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