NEET UG · Biology · Environmental Issues

Ozone Depletion: NEET previous year questions

This topic’s chapter, Environmental Issues, is not in the NEET UG 2026 syllabus. It had 5 questions from 2017 to 2023; they are kept here for reference.

Asked in 10 years: 5; about 0.5 per paper
Years asked: 4/10; last asked 2023
Syllabus: Dropped; not in NEET UG 2026
Last asked: 2023; 3 papers ago

Key findings

01
Asked in 4 of 10 papers, 5 questions in all: #156 of 204 topics by ten-year total. It comes back every 1.7 years on average. Last asked in 2023.
02
80% of its questions since 2018 tested an idea never asked before; none repeated an idea from the year before.
03
The most repeated idea is Dobson Units, asked 2 times (2021, 2023), usually as “definition recall”.
04
NEET has asked 4 of the 90 ideas in this topic; 84 have never been asked, directly or indirectly.
05
Mostly asked as one-line MCQ (100%); 100% easy, 0% hard, and down from 0.7 to 0.0 questions a paper since 2024.

Questions per year

Up to 2023: 0.7; per paper
Since 2024: 0.0; -0.7
Usual gap: 1.7 yrs; between papers asking it
Swing: ±0.7; questions, year to year

How it is asked

Difficulty, format and skill

Across all 5 questions on Ozone Depletion since 2017.

Difficulty

QUESTIONS

Easy5 · 100%
Medium0 · 0%
Hard0 · 0%

Format

One-line MCQ · 5 Q100%

Skill tested

Recall · 5 Q100%

Repeats

New idea, or one asked before?

Each column is a paper. Blue questions tested an idea NEET had not asked before; navy ones went back to an idea from an earlier paper. 2017 is the first paper, so everything in it counts as new.

’17’18’19’20’21’22’23’24’25’26

Idea asked for the first time
Idea asked in an earlier paper

Coverage of the topic

NEET has asked 4 of the 90 ideas in this topic. 84 have never been asked yet.

Asked directly4 · 4%
Touched inside another question2 · 2%
Never asked84 · 93%

Ideas come from Lumi’s syllabus map of NCERT. A never-asked idea is not a safe skip: most new questions come from exactly these.

Drill down

Idea, year, question

Every idea NEET tested in this topic, with its ten papers. Open one to read the questions.

ideaAskedShareYears’17’18’19’20’21’22’23’24’25’26

Repeated2 · 40%40%2/10
- 2023 · Q105
  The thickness of ozone in a column of air in the atmosphere is measured in terms of :
  easyOne-line MCQ
- 2021 · Q177
  Dobson units are used to measure thickness of :
  easyOne-line MCQNew idea
1 · 20%20%1/10
1 · 20%20%1/10
1 · 20%20%1/10

Squares are the ten papers, 2017 to 2026; darker means more questions. Share is of the level above.

Ideas

Every idea inside this topic

4 different ideas were tested; 1 came more than once. Montreal Protocol is the foundation for 10 other ideas in the syllabus.

Dobson Units2×
definition recall
One-line MCQ · 4% next · foundation for 6
Montreal Protocol1×
identify purpose of environmental protocol
One-line MCQ · 4% next · foundation for 10
Snow Blindness Pathology1×
identify cause of uv-b effect
One-line MCQ · 4% next · foundation for 4
Chlorine's Catalytic Nature1×
identify agent in a process
One-line MCQ · 4% next · foundation for 2

Idea	Times	Format	Chance next	Foundation for
Dobson Unitsdefinition recall	2	One-line MCQRecall	4%	6 ideas
Montreal Protocolidentify purpose of environmental protocol	1	One-line MCQRecall	4%	10 ideas
Snow Blindness Pathologyidentify cause of uv-b effect	1	One-line MCQRecall	4%	4 ideas
Chlorine's Catalytic Natureidentify agent in a process	1	One-line MCQRecall	4%	2 ideas

Chance next is the historical rate at which an idea with this record came back in the following paper. It is low for every idea, which is why learning the topic beats memorising past questions. All repeated ideas

Every question

Ozone Depletion questions, year by year

The opening words of each question as it appeared in the official paper, with the idea it tested.

NEET 20231 question

Q105
The thickness of ozone in a column of air in the atmosphere is measured in terms of :
Idea: Dobson Units
EasyOne-line MCQ

NEET 20211 question

Q177
Dobson units are used to measure thickness of :
Idea: Dobson Units
New ideaEasyOne-line MCQ

NEET 20202 questions

Q56
Montreal protocol was signed in 1987 for control of :
Idea: Montreal Protocol
New ideaEasyOne-line MCQ
Q90
Snow-blindness in Antarctic region is due to :
Idea: Snow Blindness Pathology
New ideaEasyOne-line MCQ

NEET 20181 question

Q116
In stratosphere, which of the following elements acts as a catalyst in degradation of ozone and release of molecular oxygen ?
Idea: Chlorine's Catalytic Nature
New ideaEasyOne-line MCQ

Questions from the official NEET UG papers published by NTA (CBSE before 2019). Topic and idea tags, counts and notes are Lumi’s.