NCERT Solutions for Class 11 Geography Chapter 10: Water in the Atmosphere

These Class 11 Geography Chapter 10 solutions cover Water in the Atmosphere from Fundamentals of Physical Geography, the NCERT textbook continued for the 2026–27 session. The chapter explains how water vapour enters the air through evaporation and transpiration, how it is measured as humidity (absolute and relative), how it leaves the air through condensation in forms such as dew, frost, fog, mist and clouds, and how the moisture finally returns to the surface as precipitation (rain, snow, sleet and hail). Below you get verbatim NCERT exercise questions with step-by-step, exam-ready answers, plus key terms, extra practice, MCQs, Assertion–Reason questions and FAQs.

Class: 11 Subject: Geography Book: Fundamentals of Physical Geography Chapter: 10 Chapter Name: Water in the Atmosphere Session: 2026–27
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Class 11 Geography Chapter 10 – Overview

Chapter 10, Water in the Atmosphere, studies the water vapour content of the air and the changes it undergoes. Water exists in the atmosphere in three states — gaseous, liquid and solid — and forms 0 to 4 per cent of the atmosphere by volume. It is added by evaporation from water bodies and transpiration from plants, and is removed by condensation and precipitation, keeping up a continuous exchange of water between the atmosphere, oceans and continents. The chapter defines humidity (absolute, relative, specific), saturation and dew point; explains the forms of condensation (dew, frost, fog, mist and clouds) and the four basic cloud types (cirrus, cumulus, stratus, nimbus); and describes the forms of precipitation (rainfall, snowfall, sleet, hail) and the three types of rainfall — convectional, orographic and cyclonic. It closes with the world distribution of rainfall, showing how rainfall generally decreases from the equator towards the poles.

Key Terms & Concepts

Humidity: the water vapour present in the air. It can be expressed as absolute humidity, relative humidity or specific humidity.

Absolute humidity: the actual amount (weight) of water vapour present per unit volume of air, expressed in grams per cubic metre. It differs from place to place.

Relative humidity: the percentage of moisture present in the air compared to its full capacity at a given temperature. It changes when air temperature changes; it is greater over oceans and least over continents.

Saturation & dew point: air holding moisture to its full capacity at a given temperature is saturated; the temperature at which saturation occurs (and condensation begins) is the dew point.

Evaporation: the process by which water changes from the liquid to the gaseous state. Heat is its main cause; greater air movement and lower moisture content increase it.

Latent heat of vaporisation: the heat energy required to convert a unit mass of liquid into vapour without a change in temperature.

Condensation: the transformation of water vapour into water, caused by loss of heat. In free air it forms around tiny hygroscopic condensation nuclei (dust, smoke, salt).

Forms of condensation: dew (water droplets on cold surfaces; dew point above freezing), frost (ice crystals; dew point at/below freezing), fog (cloud near the ground, visibility under 1 km), mist (visibility 1–2 km, more moisture than fog), and clouds.

Cloud types: by height and form, the four basic clouds are cirrus (high, 8,000–12,000 m, feathery, white), cumulus (cotton-wool, 4,000–7,000 m, flat base), stratus (layered, large sky cover) and nimbus (dark, dense, rain-bearing).

Precipitation: the release of moisture from the atmosphere after condensation — as rainfall, snowfall (below 0°C, hexagonal crystals), sleet (frozen raindrops/refrozen melted snow) or hail (rounded ice with concentric layers).

Types of rainfall: convectional (heated, rising air; equatorial regions), orographic / relief (air forced up a mountain; windward wet, leeward dry — the rain-shadow), and cyclonic / frontal (associated with cyclones).

NCERT Exercises — Full Solutions

All questions below are reproduced verbatim from the NCERT textbook’s end-of-chapter Exercises. Answers are original, written in exam-ready style.

1. Multiple choice questions.

(i) Which one of the following is the most important constituent of the atmosphere for human beings? (a) Water vapour    (b) Nitrogen    (c) Dust particle    (d) Oxygen

ANSWER (d) Oxygen. Human beings depend on oxygen for respiration, which makes it the most important atmospheric constituent for survival.

(ii) Which one of the following process is responsible for transforming liquid into vapour? (a) Condensation    (b) Transpiration    (c) Evaporation    (d) Precipitation

ANSWER (c) Evaporation. Evaporation is the process by which water is transformed from the liquid state into the gaseous (vapour) state, with heat as its main cause.

(iii) The air that contains moisture to its full capacity : (a) Relative humidity    (b) Specific humidity    (c) Absolute humidity    (d) Saturated air

ANSWER (d) Saturated air. Air holding moisture to its full capacity at a given temperature is said to be saturated; it cannot hold any additional moisture at that temperature.

(iv) Which one of the following is the highest cloud in the sky? (a) Cirrus    (b) Stratus    (c) Nimbus    (d) Cumulus

ANSWER (a) Cirrus. Cirrus clouds form at high altitudes of about 8,000–12,000 m, making them the highest of the four basic cloud types.

2. Answer the following questions in about 30 words.

(i) Name the three types of precipitation.

ANSWER On the basis of origin, rainfall (precipitation) is classified into three main types: convectional rain, orographic or relief rain, and cyclonic or frontal rain.

(ii) Explain relative humidity.

ANSWER Relative humidity is the percentage of moisture present in the atmosphere compared with its full capacity at a given temperature. As air temperature changes, its moisture-holding capacity changes, so relative humidity also varies. It is greater over oceans and least over continents.

(iii) Why does the amount of water vapour decreases rapidly with altitude?

ANSWER The amount of water vapour decreases rapidly with altitude because the moisture is derived from the surface (water bodies and plants) and temperature falls as we go higher. Cooler air has a much lower capacity to hold water vapour, so moisture is concentrated in the lower layers of the atmosphere.

(iv) How are clouds formed? Classify them.

ANSWER A cloud is a mass of minute water droplets or tiny ice crystals formed by the condensation of water vapour in free air at considerable elevations, around condensation nuclei. According to their height, expanse, density and transparency, clouds are grouped into four types: cirrus, cumulus, stratus and nimbus.

3. Answer the following questions in about 150 words.

(i) Discuss the salient features of the world distribution of precipitation.

ANSWER Different places receive different amounts of rainfall in different seasons. In general, rainfall decreases steadily from the equator towards the poles. Coastal areas receive more rain than the interiors, and the oceans receive more than the landmasses because they are great sources of water. Between latitudes 35° and 40° N and S, rain is heavier on the eastern coasts and decreases westward; but between 45° and 65° N and S, the westerlies bring rain first to the western margins, decreasing eastward. Where mountains run parallel to the coast, the windward coastal plains are wetter and the leeward side drier. By annual amount: the equatorial belt, the windward western slopes of cool-temperate mountains and the monsoon coasts get heavy rainfall of over 200 cm; continental interiors get 100–200 cm; central tropical lands and eastern/interior temperate lands get 50–100 cm; and rain-shadow interiors and high latitudes get less than 50 cm per year.

(ii) What are forms of condensation? Describe the process of dew and frost formation.

ANSWER Forms of condensation: After condensation, the moisture in the atmosphere takes one of the following forms — dew, frost, fog and clouds (with mist closely related to fog). They are classified on the basis of temperature and location. Dew: When moisture is deposited as water droplets on cooler surfaces of solid objects such as stones, grass blades and plant leaves (rather than on nuclei in the air), it is called dew. The ideal conditions are a clear sky, calm air, high relative humidity, and cold and long nights. For dew to form, the dew point must be above the freezing point. Frost: Frost forms on cold surfaces when condensation takes place below the freezing point (0°C), i.e. when the dew point is at or below freezing. The excess moisture is then deposited in the form of minute ice crystals instead of water droplets. The ideal conditions are the same as those for dew, except that the air temperature must be at or below the freezing point.

Project Work

Browse through the newspaper from 1st June to 31st December and note the news about extreme rainfall in different parts of the country.

HOW TO DO IT This is a hands-on project, so your record will be your own. Maintain a dated logbook or table; for each report, note the date, place/state, the amount of rainfall (in mm/cm, as reported by the IMD), and the impact (floods, landslides, waterlogging, crop loss, etc.). A suggested format to record your findings:
DatePlace / StateRainfall reportedImpact / Remarks
e.g. 26 JulyMumbai, Maharashtra~300 mm in 24 hrsWaterlogging, trains delayed
…………
At the end, summarise which months and regions had the most extreme rainfall and relate it to the south-west monsoon (June–September) and retreating monsoon (October–December) you have studied.

Extra Practice Questions

Short Answer Type Questions

Q1. Define dew point.

ANSWERThe dew point is the temperature at which saturation occurs in a given sample of air. When air is cooled to its dew point, it can no longer hold all its water vapour and condensation begins.

Q2. Distinguish between fog and mist.

ANSWERBoth are clouds near the ground. Fog reduces horizontal visibility to less than 1 km, while mist limits it to between 1 km and 2 km. Mist contains more moisture than fog and is drier in fog; mists are frequent over mountains, while fogs are common where warm and cold air currents meet.

Q3. What is latent heat of vaporisation?

ANSWERLatent heat of vaporisation is the amount of heat energy required to convert a unit mass of a liquid into vapour without any change in its temperature. This heat is absorbed during evaporation and released back during condensation.

Q4. How is sleet formed?

ANSWERSleet is frozen raindrops or refrozen melted snow-water. It forms when a layer of air above freezing point overlies a sub-freezing layer near the ground; raindrops leaving the warmer air encounter the colder air, solidify, and reach the ground as small pellets of ice.

Q5. What is a rain-shadow area?

ANSWERA rain-shadow area is the region on the leeward side of a mountain that receives very little rainfall. After giving rain on the windward side, the descending winds on the leeward slope warm up, their moisture-holding capacity rises, and so they remain dry.

Long Answer Type Questions

Q1. Explain the factors that influence the rate of evaporation and the process of condensation.

ANSWEREvaporation transforms water from the liquid to the gaseous state and is mainly caused by heat. A rise in temperature increases the air’s capacity to absorb and retain moisture, so evaporation increases. When the moisture content of the air is low, it has greater potential to absorb moisture, again raising evaporation. The movement of air also matters: it replaces a saturated layer with an unsaturated one, so the greater the movement of air, the greater the evaporation. Condensation is the reverse — the transformation of water vapour into water due to the loss of heat. When moist air is cooled to a level where it can no longer hold its vapour, the excess condenses around tiny hygroscopic nuclei such as dust, smoke and salt. Condensation also occurs when moist air touches a colder object or when the temperature is close to the dew point. It depends on the amount of cooling and the relative humidity, and is influenced by the volume, temperature, pressure and humidity of the air — the most favourable condition being a decrease in air temperature.

Q2. Describe the four basic types of clouds.

ANSWERClouds are classified by height, expanse, density and transparency into four basic types. Cirrus clouds form at high altitudes of 8,000–12,000 m; they are thin, detached, feathery and always white. Cumulus clouds look like cotton wool, form at about 4,000–7,000 m, exist in patches scattered here and there, and have a flat base. Stratus clouds are layered clouds covering large portions of the sky, generally formed by loss of heat or the mixing of air masses of different temperatures. Nimbus clouds are black or dark grey, forming at middle levels or very near the surface; they are extremely dense and opaque to the sun’s rays and appear as shapeless masses of thick vapour bringing rain. A combination of these basic types gives high clouds (cirrostratus, cirrocumulus), middle clouds (altostratus, altocumulus), low clouds (stratocumulus, nimbostratus) and clouds of great vertical development (cumulonimbus).

Q3. Describe the three types of rainfall on the basis of their origin.

ANSWERConvectional rain: When air is heated it becomes light and rises in convection currents; as it rises it expands, cools, and condensation forms cumulus clouds. With thunder and lightning, heavy but short-lived rain falls. It is common in summer and in the hotter part of the day, especially in equatorial regions and continental interiors. Orographic (relief) rain: When a saturated air mass meets a mountain it is forced to ascend, expands, cools and its moisture condenses, so the windward slopes receive heavy rain. After crossing the mountain, the descending winds on the leeward side warm up and remain dry, creating a rain-shadow area. Cyclonic (frontal) rain: This is associated with cyclones — rising warm, moist air along fronts cools and condenses to give rainfall, as with the extra-tropical cyclones studied earlier. Together, these three mechanisms account for most of the rainfall received on the earth’s surface.

MCQs & Assertion–Reason

1. Water vapour forms what percentage of the atmosphere by volume?

(a) 0 to 4 per cent    (b) 5 to 10 per cent    (c) 10 to 15 per cent    (d) 21 per cent

2. The actual amount of water vapour present per unit volume of air is called:

(a) relative humidity    (b) absolute humidity    (c) specific humidity    (d) dew point

3. The temperature at which saturation occurs in a given sample of air is the:

(a) freezing point    (b) latent heat    (c) dew point    (d) boiling point

4. Tiny particles of dust, smoke and salt around which condensation occurs are called:

(a) aerosols    (b) hygroscopic condensation nuclei    (c) ions    (d) hailstones

5. Frost forms when condensation takes place:

(a) above the freezing point    (b) at or below the freezing point    (c) at 100°C    (d) over oceans only

6. Fog reduces horizontal visibility to less than:

(a) 5 km    (b) 2 km    (c) 1 km    (d) 100 m

7. Cumulus clouds are generally formed at a height of:

(a) 4,000–7,000 m    (b) 8,000–12,000 m    (c) below 1,000 m    (d) above 15,000 m

8. Frozen raindrops and refrozen melted snow-water form:

(a) hail    (b) sleet    (c) dew    (d) frost

9. The rainless dry area on the leeward side of a mountain is called the:

(a) windward slope    (b) rain-shadow area    (c) convection zone    (d) front

10. As we proceed from the equator towards the poles, rainfall generally:

(a) increases steadily    (b) decreases steadily    (c) remains constant    (d) becomes zero everywhere

Answer key: 1-(a), 2-(b), 3-(c), 4-(b), 5-(b), 6-(c), 7-(a), 8-(b), 9-(b), 10-(b).

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: The greater the movement of air, the greater is the evaporation.

Reason: Moving air replaces the saturated layer with an unsaturated layer, allowing more moisture to be absorbed.

A-R 2. Assertion: For the formation of dew, the dew point must be above the freezing point.

Reason: If the dew point is at or below freezing, moisture is deposited as ice crystals (frost) instead of water droplets.

A-R 3. Assertion: Relative humidity is greater over the oceans than over the continents.

Reason: Oceans are large sources of water and add abundant moisture to the air above them.

A-R 4. Assertion: The windward slopes of mountains receive greater orographic rainfall.

Reason: Saturated air forced up a mountain expands, cools and its moisture condenses on the windward side.

A-R 5. Assertion: Cirrus clouds are dark, dense, rain-bearing clouds near the ground.

Reason: Cirrus clouds form at high altitudes of 8,000–12,000 m and are thin, feathery and white.

Answer key: 1-(A), 2-(A), 3-(A), 4-(A), 5-(D).

Exam Tips & Common Mistakes

How to score full marks in this chapter

Memorise the precise definitions of absolute humidity, relative humidity, saturation and dew point — they are frequent one-mark questions. For condensation, link each form (dew, frost, fog, mist) to its temperature condition and visibility figure. Tabulate the four cloud types with their height ranges and appearance, and the four forms of precipitation. For the long answers on rainfall types and world distribution, use the textbook’s exact figures (over 200 cm, 100–200 cm, 50–100 cm, less than 50 cm; latitudes 35°–40° and 45°–65°). Always mention the windward/leeward (rain-shadow) contrast in orographic rain.

Common mistakes to avoid

  • Confusing absolute humidity (g/m³, actual amount) with relative humidity (a percentage of capacity).
  • Mixing up dew (above freezing, water droplets) and frost (at/below freezing, ice crystals).
  • Swapping the visibility figures for fog (under 1 km) and mist (1–2 km).
  • Calling cirrus a low rain cloud — it is the highest cloud; nimbus is the dark rain-bearing one.
  • Saying rainfall increases towards the poles — it generally decreases steadily towards the poles.
  • Forgetting that the most favourable condition for condensation is a decrease in air temperature.

Frequently Asked Questions

What is Chapter 10 of Class 11 Geography about?

Chapter 10, Water in the Atmosphere, from Fundamentals of Physical Geography explains how water vapour enters the air by evaporation and transpiration, how humidity is measured, how condensation produces dew, frost, fog, mist and clouds, and how precipitation occurs as rain, snow, sleet and hail, ending with the world distribution of rainfall.

What is the difference between absolute and relative humidity?

Absolute humidity is the actual weight of water vapour per unit volume of air, measured in grams per cubic metre. Relative humidity is the percentage of moisture present compared with the air’s full capacity at a given temperature, so it changes whenever the temperature changes.

What are the three types of rainfall?

On the basis of origin, rainfall is of three types: convectional rain (heated, rising air), orographic or relief rain (air forced up a mountain, with a wet windward side and dry leeward rain-shadow), and cyclonic or frontal rain (associated with cyclones).

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