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Q12 (IAS/2024) Geography › World Physical Geography › Atmosphere composition Official Key

With reference to "water vapour", which of the following statements is/are correct ? 1. It is a gas, the amount of which decreases with altitude. 2. Its percentage is maximum at the poles. Select the answer using the code given below :

Result
Your answer: —  ·  Correct: A
Explanation

The correct answer is option A (1 only).

**Statement 1 is correct:** Water vapour is a variable gas in the atmosphere, which decreases with altitude.[1] Additionally, 90% of moisture content in the atmosphere exists within 6 km of the surface of the earth.[2] This clearly confirms that the amount of water vapour decreases as we move higher in the atmosphere.

**Statement 2 is incorrect:** In the warm and wet tropics, water vapour may account for four per cent of the air by volume, while in the dry and cold areas of desert and polar regions, it may be less than one per cent of the air. Water vapour also decreases from the equator towards the poles.[1] This demonstrates that water vapour percentage is actually minimum at the poles, not maximum. The maximum concentration occurs in warm, tropical regions where evaporation rates are highest.

Therefore, only statement 1 is correct, making option A the right answer.

Sources
  1. [1] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 7: Composition and Structure of Atmosphere > Water Vapour > p. 64
  2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Water Vapour > p. 272
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Don’t just practise – reverse-engineer the question. This panel shows where this PYQ came from (books / web), how the examiner broke it into hidden statements, and which nearby micro-concepts you were supposed to learn from it. Treat it like an autopsy of the question: what might have triggered it, which exact lines in the book matter, and what linked ideas you should carry forward to future questions.
Q. With reference to "water vapour", which of the following statements is/are correct ? 1. It is a gas, the amount of which decreases with …
At a glance
Origin: Books + Current Affairs Fairness: Moderate fairness Books / CA: 6.7/10 · 3.3/10

This is a textbook 'Sitter' directly from NCERT Class XI Physical Geography. It penalizes aspirants who skim basic chapters like 'Composition of Atmosphere' to rush towards complex climatology. If you missed this, your static foundation has cracks.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
Is water vapour the gaseous phase of water in Earth's atmosphere?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Science-Class VII . NCERT(Revised ed 2025) > Chapter 7: Heat Transfer in Nature > 7.4 Water Cycle > p. 98
Presence: 5/5
“You have also learnt in the Grade 6 Science textbook Curiosity, that water exists in three states in nature. As a liquid, it fi lls the oceans, rivers, and lakes on the Earth. As a solid, it forms snow, ice sheets, and glaciers in the mountains and the polar regions. As a gas, it exists in the form of water vapour in the Earth's atmosphere. During summers, some of the snow and ice gets converted to water due to the Sun's radiation and fl ows down as rivers, and ultimately into the oceans. The melted ice is replenished by fresh snow during winters.”
Why this source?
  • Explicitly identifies water vapour as the form in which water exists as a gas in the Earth's atmosphere.
  • Places this gaseous form within the context of the water cycle and the three physical states of water on Earth.
Exploring Society:India and Beyond ,Social Science-Class VII . NCERT(Revised ed 2025) > Chapter 2: Understanding the Weather > Water vapour: > p. 29
Presence: 5/5
“Water vapour is water in gaseous instead of liquid form.”
Why this source?
  • Defines water vapour as water in the gaseous rather than liquid form.
  • Provides a clear, direct definition linking 'water vapour' to the gaseous phase.
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 10: Water in the Atmosphere > CHAPTER > p. 86
Presence: 5/5
“Y ou have already learnt that the air contains water vapour. It varies from zero to four per cent by volume of the atmosphere and plays an important role in the weather phenomena. Water is present in the atmosphere in three forms namely – gaseous, liquid and solid. The moisture in the atmosphere is derived from water bodies through evaporation and from plants through transpiration. Thus, there is a continuous exchange of water between the atmosphere, the oceans and the continents through the processes of evaporation, transpiration, condensation and precipitation. Water vapour present in the air is known as humidity.”
Why this source?
  • States that water in the atmosphere occurs in three forms, explicitly including the gaseous form.
  • Links atmospheric moisture and the term 'water vapour' to the gaseous state of water (humidity).
Statement 2
Does the concentration (amount) of water vapour in Earth's atmosphere generally decrease with altitude?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 7: Composition and Structure of Atmosphere > Water Vapour > p. 64
Presence: 5/5
“Water vapour is also a variable gas in the atmosphere, which decreases with altitude. In the warm and wet tropics, it may account for four per cent of the air by volume, while in the dry and cold areas of desert and polar regions, it may be less than one per cent of the air. Water vapour also decreases from the equator towards the poles. It also absorbs parts of the insolation from the sun and preserves the earth's radiated heat. It thus, acts like a blanket allowing the earth neither to become too cold nor too hot. Water vapour also contributes to the stability and instability in the air.”
Why this source?
  • Directly states that water vapour is a variable gas which decreases with altitude.
  • Contrasts higher moisture in warm/tropical regions with much lower values in cold/dry regions, implying concentration is greatest near the surface.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 22: Vertical Distribution of Temperature > 22.2. Lapse Rate > p. 295
Presence: 5/5
“Hence, the lapse rate of the troposphere below tropopause is positive, the lapse rate of the tropopause is zero, and the lapse rate of the stratosphere is negative.• The fall in temperature with altitude is primarily due to the following reason: • Atmosphere is mostly transparent to the incoming shortwave radiation but actively absorbs the outgoing terrestrial (longwave) radiation.• Greenhouse house gases like CO2, and water vapour, are the primary absorbers of terrestrial radiation and their concentration is highest at the earth's surface and goes on decreasing with altitude. Hence, the temperature falls with altitude (elevation).• The lapse rate of non-rising air (environmental lapse rate) is highly variable, being affected by radiation, convection, condensation and concentration of greenhouse gases.”
Why this source?
  • Explains that greenhouse gases including water vapour have highest concentration at the surface and decrease with altitude.
  • Links the vertical decrease of these gases to the lapse rate and falling temperature with height, strengthening causal basis.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Water Vapour > p. 272
Presence: 5/5
“• Water Vapour is one of the most variable gaseous substances present in the atmosphere constituting between 0.02% and 4% of the total volume (in cold dry, and humid tropical climates, respectively).• 90% of moisture content in the atmosphere exists within 6 km of the surface of the earth. Like carbon dioxide, water vapour plays a significant role in the insulating action, of the atmosphere. It absorbs not only the long-wave terrestrial radiation (infrared or heat emitted by the earth during the nights) but also a part of the incoming short-wave solar radiation (visible and UV radiation).”
Why this source?
  • Quantifies moisture distribution by stating about 90% of atmospheric moisture exists within 6 km of the surface, implying steep decline above.
  • Provides volumetric range for water vapour (0.02%–4%), supporting the idea of concentrated near-surface moisture.
Statement 3
Is the percentage (concentration) of water vapour in Earth's atmosphere highest at the poles?
Origin: Web / Current Affairs Fairness: CA heavy Web-answerable

Web source
Presence: 5/5
"atmospheric concentration of water vapour is highly variable between locations and times, from 10 ppmv in the coldest air to 5% (50 000 ppmv) in humid tropical air,"
Why this source?
  • Gives numeric range of water-vapour concentration from the coldest air to humid tropical air.
  • Explicitly shows the highest concentrations occur in humid tropical air and the lowest in the coldest air — implying poles are not where water vapour is highest.
Web source
Presence: 4/5
"The percentage of water vapor in surface air varies from 0.01% at -42 °C (-44 °F)[18] to 4.24% when the dew point is 30 °C (86 °F).[19]"
Why this source?
  • Provides concrete surface-air percentage extremes tied to temperature.
  • Shows very low percentage (0.01%) at −42 °C versus much higher (4.24%) at warm dew points — supporting that colder regions (like poles) have much lower water vapour.
Web source
Presence: 4/5
"Because warmer air holds more moisture, its concentration of water vapor increases."
Why this source?
  • Explains the basic physical relationship: warmer air holds more moisture, so water-vapour concentration increases with temperature.
  • Implying regions that are warmer (tropics) have higher water vapour than cold polar regions.

FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 7: Composition and Structure of Atmosphere > Water Vapour > p. 64
Strength: 5/5
“Water vapour is also a variable gas in the atmosphere, which decreases with altitude. In the warm and wet tropics, it may account for four per cent of the air by volume, while in the dry and cold areas of desert and polar regions, it may be less than one per cent of the air. Water vapour also decreases from the equator towards the poles. It also absorbs parts of the insolation from the sun and preserves the earth's radiated heat. It thus, acts like a blanket allowing the earth neither to become too cold nor too hot. Water vapour also contributes to the stability and instability in the air.”
Why relevant

States water vapour decreases from the equator towards the poles and is less than 1% in polar regions versus up to 4% in warm tropics.

How to extend

A student can combine this with the basic fact that the poles are cold (less evaporation) to infer poles are unlikely to have the highest concentration.

Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Water Vapour > p. 272
Strength: 5/5
“• Water Vapour is one of the most variable gaseous substances present in the atmosphere constituting between 0.02% and 4% of the total volume (in cold dry, and humid tropical climates, respectively).• 90% of moisture content in the atmosphere exists within 6 km of the surface of the earth. Like carbon dioxide, water vapour plays a significant role in the insulating action, of the atmosphere. It absorbs not only the long-wave terrestrial radiation (infrared or heat emitted by the earth during the nights) but also a part of the incoming short-wave solar radiation (visible and UV radiation).”
Why relevant

Gives the range of water vapour (0.02%–4%) and explicitly ties the high end to humid tropical climates and low end to cold dry climates.

How to extend

Using a world map to locate tropical vs polar climates, one can expect higher values in the tropics and lower at the poles.

Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 24: Hydrological Cycle (Water Cycle) > Absolute Humidity > p. 326
Strength: 4/5
“• The actual amount of water vapour present in the atmosphere is known as absolute humidity. It is the weight of water vapour per unit volume of air and is expressed in grams per cubic metre.• The absolute humidity differs from place to place on the earth's surface. Absolute humidity is greater over oceans because of the greater availability of water for evaporation.• The ability of the air to hold water vapour depends entirely on its temperature. Warm air can hold more moisture than cold air. Cold air is mostly dry as water vapour condenses into dew, snow and other forms and falls to the ground.”
Why relevant

Explains absolute humidity is greater over oceans (more evaporation) and that warm air holds more moisture while cold air is mostly dry.

How to extend

A student could note the poles have low temperatures and limited open-water evaporation, so would likely have lower absolute humidity than warmer regions.

Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 24: Hydrological Cycle (Water Cycle) > Water Vapour In Atmosphere > p. 325
Strength: 4/5
“• Water vapour in air varies from zero to four per cent by volume of the atmosphere (averaging around 2% in the atmosphere). The amount of water vapour in the atmosphere (humidity) is measured by a hygrometer.”
Why relevant

Gives a numerical range for atmospheric water vapour (0–4%, average ~2%), showing significant geographic variability.

How to extend

Comparing average global values to the low polar values cited elsewhere would support judging that poles are not the maximum.

Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Explanation: > p. 276
Strength: 3/5
“• The stratosphere is very dry and contains little water vapour. Because of this, few clouds are found in this layer. Polar stratospheric clouds (PSCs) are the exception. PSCs appear in the lower stratosphere near the poles in winter.• Since the statement is absolute (no clouds or water vapour), the answer is debatable between (b) 2 only and (c) Both.”
Why relevant

Notes the stratosphere is very dry with little water vapour, except for polar stratospheric clouds which are exceptions near the poles in winter.

How to extend

A student could distinguish between general atmospheric humidity (troposphere) and rare stratospheric phenomena, avoiding conflating occasional polar clouds with generally high polar vapour concentration.

Pattern takeaway: UPSC 2024 signaled a 'Return to Basics'. While aspirants were studying complex phenomena like 'Atmospheric Rivers', the commission asked a fundamental static question about water vapour distribution. Master the NCERT lines on spatial and vertical distribution before touching reference books.
How you should have studied
  1. [THE VERDICT]: Sitter. Verbatim lift from NCERT Class XI Fundamentals of Physical Geography, Chapter 7 (Composition and Structure of Atmosphere), Page 64.
  2. [THE CONCEPTUAL TRIGGER]: Climatology > Atmospheric Composition > Variable Gases (Water Vapour, CO2, Ozone, Dust).
  3. [THE HORIZONTAL EXPANSION]: Memorize the 'Sibling Variable Gases': (1) Dust Particles: Higher concentration in subtropical/temperate dry winds, lower in equatorial/polar regions; act as hygroscopic nuclei. (2) CO2: Transparent to incoming solar, opaque to outgoing terrestrial. (3) Ozone: Max concentration at 20-25km height. (4) Homosphere (up to 80km) vs Heterosphere (above 80km).
  4. [THE STRATEGIC METACOGNITION]: When NCERT describes a physical quantity (temp, salinity, density, gas), always map its 'Gradient': Does it increase/decrease with Altitude? Does it increase/decrease from Equator to Poles? UPSC loves swapping these trends.
Concept hooks from this question
📌 Adjacent topic to master
S1
👉 States of water in the atmosphere
💡 The insight

Water in the atmosphere occurs as gas, liquid and solid, so identifying water vapour means recognizing the gaseous state.

High-yield for physical geography and environment questions: it underpins topics like the water cycle, precipitation processes and atmospheric moisture. Mastery helps answer questions on phase changes, humidity, and weather phenomena.

📚 Reading List :
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 10: Water in the Atmosphere > CHAPTER > p. 86
  • Science-Class VII . NCERT(Revised ed 2025) > Chapter 7: Heat Transfer in Nature > 7.4 Water Cycle > p. 98
  • Exploring Society:India and Beyond ,Social Science-Class VII . NCERT(Revised ed 2025) > Chapter 2: Understanding the Weather > Water vapour: > p. 29
🔗 Anchor: "Is water vapour the gaseous phase of water in Earth's atmosphere?"
📌 Adjacent topic to master
S1
👉 Humidity and spatial/temperature controls on water vapour
💡 The insight

The amount of water vapour varies by location and temperature, defining humidity and its measurement.

Crucial for questions on climate zones, hydrology and meteorology; links to concepts such as absolute humidity, hygrometers, altitude effects and why warm air holds more moisture. Enables explanation of regional climate differences and monsoon dynamics.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Water Vapour > p. 272
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 7: Composition and Structure of Atmosphere > Water Vapour > p. 64
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 24: Hydrological Cycle (Water Cycle) > Absolute Humidity > p. 326
🔗 Anchor: "Is water vapour the gaseous phase of water in Earth's atmosphere?"
📌 Adjacent topic to master
S1
👉 Water vapour's role in Earth's energy balance
💡 The insight

Water vapour absorbs terrestrial radiation and contributes to the greenhouse effect, affecting Earth's temperature regulation.

Important for environment and climate-change questions; connects atmospheric composition to radiative forcing, feedbacks with CO2, and policy discussions on greenhouse gases. Helps in framing answers on climate feedback mechanisms and warming patterns.

📚 Reading List :
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Water Vapour > p. 272
  • Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 17: Climate Change > r7.3.r. Water vapour > p. 255
🔗 Anchor: "Is water vapour the gaseous phase of water in Earth's atmosphere?"
📌 Adjacent topic to master
S2
👉 Vertical distribution of water vapour
💡 The insight

Water vapour concentration declines with height, with most atmospheric moisture confined to the lower troposphere.

High-yield for explaining humidity profiles, cloud formation zones, and why weather phenomena are concentrated near the surface; links to troposphere structure and weather systems. Mastery helps answer questions on moisture availability with altitude, precipitation processes, and climatic gradients.

📚 Reading List :
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 7: Composition and Structure of Atmosphere > Water Vapour > p. 64
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 22: Vertical Distribution of Temperature > 22.2. Lapse Rate > p. 295
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Water Vapour > p. 272
🔗 Anchor: "Does the concentration (amount) of water vapour in Earth's atmosphere generally ..."
📌 Adjacent topic to master
S2
👉 Temperature control of absolute humidity
💡 The insight

Air temperature determines how much water vapour it can hold, so cooler air aloft holds less moisture.

Crucial for linking lapse rate, condensation, and relative/absolute humidity in climate and hydrology questions. Enables reasoning about why humidity drops with altitude and how temperature changes drive condensation and cloud formation.

📚 Reading List :
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 10: Water in the Atmosphere > CHAPTER > p. 86
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 24: Hydrological Cycle (Water Cycle) > Absolute Humidity > p. 326
🔗 Anchor: "Does the concentration (amount) of water vapour in Earth's atmosphere generally ..."
📌 Adjacent topic to master
S2
👉 Homosphere uniformity and near-surface variability
💡 The insight

The homosphere has a nearly uniform gas mix except for variations in water vapour and pollutants concentrated in the lowest atmospheric layer.

Important for distinguishing compositional uniformity at large scale from near-surface variability that affects weather and pollution studies. Helps in answering questions on vertical composition, trace gas distributions, and impacts on surface climate.

📚 Reading List :
  • Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > Dirunion of Atmosphere > p. 7
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 7: Composition and Structure of Atmosphere > Water Vapour > p. 64
🔗 Anchor: "Does the concentration (amount) of water vapour in Earth's atmosphere generally ..."
📌 Adjacent topic to master
S3
👉 Latitudinal variation of atmospheric water vapour
💡 The insight

Water vapour concentration falls from the warm, humid tropics toward cold polar regions, where values can be much lower.

This concept explains large-scale moisture gradients that determine climate zones, precipitation patterns and impacts of latitude on humidity; mastering it helps answer questions on climate classification, regional hydrology and comparative climatology.

📚 Reading List :
  • FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 7: Composition and Structure of Atmosphere > Water Vapour > p. 64
  • Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Water Vapour > p. 272
🔗 Anchor: "Is the percentage (concentration) of water vapour in Earth's atmosphere highest ..."
🌑 The Hidden Trap

The 'Dust Particle' distribution. Just like water vapour, dust has a specific latitudinal trend: highest in Subtropical High-Pressure belts (dry winds) and lowest at the Equator (washed out by rain) and Poles. Expect a statement swapping these locations.

⚡ Elimination Cheat Code

Apply 'Climatic Common Sense'. Statement 2 claims water vapour is maximum at the poles. Poles are 'Cold Deserts'. Evaporation requires heat. No heat = minimal evaporation = minimal water vapour. It is physically impossible for the coldest region to hold the maximum gas. Eliminate Statement 2 immediately.

🔗 Mains Connection

Mains GS-3 (Environment): Water Vapour is the most potent 'Greenhouse Gas' (often ignored for CO2). Use the 'Positive Feedback Loop' concept: Warmer Earth -> More Evaporation -> More Water Vapour -> More Heat Trapped -> More Warming. This is crucial for Climate Change answers.

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SIMILAR QUESTIONS

CDS-II · 2025 · Q96 Relevance score: 4.46

Which of the following statements with reference to Water Vapour in the atmosphere is/are correct? 1. It has a role to play in the stability and instability in the air. 2. It acts like a blanket allowing the earth to neither become too cold nor too hot. Select the answer using the code given below:

NDA-II · 2013 · Q63 Relevance score: 0.42

Which of the following statements is/are correct? 1. Air close to the Earth’s surface heavier. 2. Air close to the Earth’s surface contains larger quantity of water vapoor and dust particles Select the correct answer using the code given below :

IAS · 2021 · Q72 Relevance score: -0.49

With reference to the water on the planet Earth, consider the following statements : 1. The amount of water in the rivers and lakes is more than the amount of groundwater. 2. The amount of water in polar ice caps and glaciers is more than the amount of groundwater. Which of the statements given above is/are correct?

IAS · 2015 · Q93 Relevance score: -1.19

With reference to bio-toilets used by the Indian Railways, consider the following statements : 1. The decomposition of human waste in the bio-toilets is initiated by a fungal inoculum. 2. Ammonia and water vapour are the only end products in this decomposition which are released into the atmosphere. Which of the statements given above is/are correct?