Natural Resources (VI–VIII) • Topic 1 of 3

Air, Water & Soil

Start with the numbers CTET expects you to know without hesitation. Air is a mixture, not a single gas: about 78% nitrogen, about 21% oxygen, and the remaining 1% is carbon dioxide, argon, water vapour and traces of other gases. Nitrogen is the most abundant — students (and weak candidates) often wrongly say oxygen, so this is a favourite trap. Air has mass and exerts pressure; the NCERT classroom demonstration is the crushed-can or the two-balloons-on-a-stick experiment showing air is matter. Water moves through the water cycle in three stages: evaporation (the Sun turns surface water into vapour), condensation (vapour cools high up and forms clouds), and precipitation (water falls back as rain, snow or hail). Transpiration from plants also adds vapour. The cycle is driven by the Sun's energy and explains why total water on Earth stays roughly constant. Soil forms slowly by weathering — the breaking down of rock by sun, water, wind and living things — over hundreds of years. A vertical cut shows the soil profile: the dark, humus-rich topsoil where most roots and organisms live; the lighter, mineral-rich subsoil; and the parent rock below. Soil is classified by particle size: sandy soil (large particles, drains quickly, poor at holding water), clayey soil (very fine particles, holds water, poorly aerated), and loamy soil (a balanced mix — the best for most crops). Pedagogy: these topics are ideal for activity-based, inquiry learning. A child should pour water through sandy and clayey samples to see percolation, not just read a table. Common misconceptions to correct: that 'air is nothing/empty', that plants take their food (not just water and minerals) from soil, and that the same amount of rain falls everywhere. How it is tested: direct fact recall (percentages, cycle order, horizons) and scenario items where a teacher designs an experiment or addresses a student's wrong idea.

✅ Solved examples

1. The most abundant gas in air, making up roughly 78% of it, is:
Nitrogen. Oxygen is second at about 21%. A common student error is to name oxygen as the most abundant — CTET tests this directly.
2. In the water cycle, the process by which water vapour cools and turns into tiny droplets forming clouds is:
Condensation. The order is evaporation (water → vapour) → condensation (vapour → droplets/clouds) → precipitation (rain/snow falls).
3. The uppermost layer of soil, rich in humus and where most plant roots grow, is called the:
Topsoil. Below it lie the subsoil and then the parent rock. Topsoil is darkest because of decayed organic matter (humus).
4. A Class VII teacher wants students to discover which soil holds the most water. The best approach is to:
Have students pour equal water through equal amounts of sandy, clayey and loamy soil and observe how much percolates — an activity/inquiry method that lets children construct the concept rather than memorise it.

✏️ Practice — try these, take hints as needed

1. Approximately what percentage of air is oxygen?
Nitrogen is ~78%.
The second most abundant gas.
About 21%
2. Name the process in the water cycle in which the Sun changes surface water into water vapour.
It is the first stage.
Liquid → gas.
Evaporation
3. Which soil type, being a balanced mixture of sand, clay and humus, is considered best for growing most crops?
Not pure sandy, not pure clayey.
Farmers prize it.
Loamy soil
4. The gradual breaking down of rocks by sun, water and wind that helps form soil is called:
A slow physical/chemical process.
Takes hundreds of years.
Weathering

📝 Topic test — 8 questions

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