1) 20 Important Words & Meanings (Meanings in Hindi)

2) Important Notes (Quick Revision)

• Air: A homogeneous mixture of gases. Air has mass, weight, volume, occupies space, and exerts atmospheric pressure (≈ \(1{,}01{,}400\,\text{N m}^{-2}\) at sea level).
• Pressure is omnidirectional: Experiments with syringes show air pressure acts equally in all directions.
• Bernoulli’s principle: When air speed increases, pressure decreases ⟶ responsible for straw-fountain, flight lift, etc.
• Humidity & condensation: Cooler air holds less vapour ⟶ dew forms; droplets appear on a cold glass by condensation.
• Winds: Flow from high pressure to low pressure areas.
• Sound transmission: Air is the common medium for sound; denser cold air can carry distant sounds more clearly.
• Water (liquid): Has definite volume and mass, no fixed shape; is a fluid, seeps through gaps, forms drops on oily surfaces.
• Freezing & density: On freezing, volume increases, so density decreases and ice floats.
• Density formula: \( \rho=\dfrac{m}{V} \) (units: \( \text{g cm}^{-3} \) or \( \text{kg m}^{-3} \)). \(1\,\text{L}=1000\,\text{cm}^3\), so pure water has \( \rho = 1\,\text{g cm}^{-3} \).
• Anomalous behaviour: Water’s density is maximum at \(4^\circ\text{C}\). Below that, it expands, so surfaces freeze while deeper water stays liquid ⟶ aquatic life survives.
• Solutions: Salt (solute) + water (solvent) → solution. Dissolving increases density (e.g., seawater \(>\) rainwater).
• Uses of water: Transport (fluidity), hydroelectricity (falling water), coolant (engines), universal solvent (industry & body processes), cleaning.
• Soil properties: Colour (black/red/yellow/grey) indicates fertility, drainage, composition; texture depends on particle sizes (sand/silt/clay).
• Soil texture: Sandy (large grains, quick drainage, low nutrients), silt (medium grains, more organic matter), clay (fine grains, high water-holding).
• Soil structure: Columnar/laminar/granular/blocky. Good structure → aeration, drainage, better root growth.
• Useful soils: China clay (kaolin), shadu (idols), terracotta (red ware), multani mitti (cosmetics).
• Soil testing: Check colour, texture, organic matter, pH, and electrical conductivity to guide fertilizer/lime use and crop planning.
• Fertility loss causes: Extreme pH, low organics, poor drainage, repeated monocropping, saline water, excessive chemicals; crop rotation restores fertility (e.g., legumes).

3) 20 Important “One-Word Answer” Type Questions

1. Which pressure do air molecules exert on bodies?
   Atmospheric pressure — acts in all directions.
2. Air at sea level exerts approximately how much pressure?
   \(1{,}01{,}400\,\text{N m}^{-2}\) (about one atmosphere).
3. Which instrument measures atmospheric pressure?
   Barometer.
4. What is the mixture type of air?
   Homogeneous mixture of gases.
5. Which principle explains the straw “water fountain”?
   Bernoulli’s principle.
6. Name the property of air responsible for winds.
   Pressure difference (air flows high → low pressure).
7. What is the process of vapour becoming liquid called?
   Condensation.
8. What do we call the moisture level of air?
   Humidity.
9. At what temperature is water’s density maximum?
   \(4^\circ\text{C}\).
10. Write the formula for density.
    \(\rho=\dfrac{m}{V}\).
11. What is the unit of density in cgs?
    g/cm³ (or g/cc).
12. Does liquid water have a fixed shape?
    No — it takes the container’s shape.
13. What do salt (NaCl) and water form on mixing?
    Solution.
14. Which soil has the highest water-holding capacity?
    Clay soil.
15. Which soil drains fastest?
    Sandy soil.
16. Name the property that lets soil be shaped into pots.
    Plasticity.
17. What does pH 7 indicate for soil?
    Neutral soil.
18. Which test helps decide fertilizer/lime needs?
    Soil testing (pH & EC).
19. Which medium generally carries sound to us?
    Air.
20. Why does ice float on water in one word?
    Lower density.

4) 20 Very Short Answer Questions

1. Why does an inflated balloon make a beam-balance tilt?
   Air has mass/weight, so the heavier (air-filled) side goes down.
2. Why does a syringe piston spring back when the inlet is closed?
   Outside air pressure is higher than the rarefied air inside, so it pushes the piston in.
3. How does temperature affect air’s moisture capacity?
   Higher temperature → higher capacity to hold vapour; low temperature → dew.
4. Why do water droplets appear outside a cold glass?
   Air near the glass cools; condensation forms droplets.
5. Define dew.
   Night/morning water droplets forming when air cools below its dew point.
6. Why do we hear distant trains clearly on winter mornings?
   Cold air is denser and carries sound more efficiently.
7. State one reason ice floats on water.
   On freezing, volume increases → density decreases.
8. Write density formula and unit.
   \(\rho=\dfrac{m}{V}\); unit g/cm³ (or kg/m³).
9. Why is swimming easier in the sea than in a well?
   Seawater is denser (dissolved salts) → more buoyancy.
10. Name the three main soil textures.
    Sandy, silt, clay.
11. Which soil is easy to plough but less fertile?
    Sandy soil — quartz grains, poor nutrients.
12. What is meant by soil structure?
    The arrangement/shape of soil particles (granular, blocky, etc.).
13. Give one benefit of good soil structure.
    Better aeration & drainage → healthy roots.
14. Name any useful special soil.
    China clay (kaolin) / shadu / terracotta / multani mitti.
15. What is the pH range for neutral soil?
    6.5 – 7.5 (about 7).
16. Name one cause of reduced soil fertility.
    Repeated monocropping / excess fertilizers / saline water.
17. State one use of water due to its fluidity.
    Water transport (boats/ships).
18. Write any one cleaning use of water.
    Bathing, washing clothes, utensils.
19. What is meant by scattering of light?
    Light spread by tiny particles in air (dust/smoke/moisture).
20. Which property of soil helps water storage in bunds?
    Water-holding capacity of soil.

5) 20 Short Answer Questions (2–3 lines)

1. Explain why air pressure acts in all directions.
   Gas molecules move randomly and strike surfaces from all sides. Experiments with syringes oriented vertically/horizontally show equal atmospheric pressure in all directions.
2. Describe Bernoulli’s principle with an example.
   When air flows faster, its pressure drops. Blowing across a straw lowers pressure at the top, so higher atmospheric pressure pushes water up → fountain.
3. How does temperature influence humidity and dew formation?
   Cool air holds less vapour; excess moisture condenses as dew at night/dawn. Warmer afternoons increase vapour capacity so air feels drier.
4. Why is water said to have definite volume but no shape?
   Liquid water maintains its volume & mass but conforms to the shape of the container due to fluidity.
5. Show that pure water has density \(1\,\text{g cm}^{-3}\).
   If \(m=1\,\text{kg}=1000\,\text{g}\) and \(V=1\,\text{L}=1000\,\text{cm}^3\), then \(\\(\\rho=\\tfrac{m}{V}=\\tfrac{1000}{1000}=1\\,\\text{g cm}^{-3}\\)
6. Why does a fully filled glass bottle crack in a freezer?
   On freezing, water’s volume increases; pressure builds up in the rigid bottle, causing it to crack/explode.
7. How does salt affect water density?
   Dissolved salt adds mass without much volume increase → density rises; hence potato floats in salt water.
8. Differentiate sandy and clay soils by any two properties.
   Sandy: large grains, quick drainage, low nutrients. Clay: fine grains, high water-holding, sticky, harder to plough.
9. What is soil structure and why is it important?
   The arrangement (granular/blocky etc.) of particles. Good structure improves aeration and drainage, enhancing root growth and fertility.
10. State two practical uses of water based on its properties.
    Hydroelectricity from falling water; coolant in engines due to high heat capacity.
11. Why is water called a universal solvent?
    Many substances dissolve in water (salts, sugars, gases), enabling industrial uses and biological processes (digestion, excretion).
12. How does air help in transmission of sound?
    Sound waves travel as pressure variations through air; without air (vacuum), sound can’t travel to us.
13. What does soil testing help farmers decide?
    It reveals pH, nutrient status, and salinity, guiding choice of fertilizers/lime and crop rotation.
14. Give two causes of declining soil fertility.
    Monocropping, poor drainage, saline irrigation, or excess chemicals disrupt soil chemistry and texture.
15. Why is ploughing clay soil difficult?
    Fine particles and high water-holding make it sticky/compact, increasing resistance to tillage.
16. Name four special soils and one use each.
    Kaolin: crockery/tiles; Shadu: idols; Terracotta: pots/decor; Multani: cosmetics.
17. What is scattering of light in air?
    Dust, smoke, and moisture particles scatter light in all directions, making beams visible.
18. Why does wind blow from sea to land sometimes?
    Due to pressure differences created by unequal heating (high → low pressure flow).
19. How does crop rotation help soil?
    Alternating with legumes adds nitrogen and breaks pest cycles, restoring fertility.
20. Why do wet clothes dry slower in monsoon?
    High humidity reduces evaporation rate; air is already moisture-laden.

6) Textbook Exercise – Perfect Answers

Colour Legend

Questions are in Red   |   Answers are in Green