Chapter 3 - Properties of Natural Resources
1. Fill in the blanks with the appropriate term.
(Temperature, volume, mass, density, humidity, acidic, weight, neutral, shape.)
(a) The capacity of air to hold moisture depends upon the ______ of the air.
Ans: humidity.
(b) Water does not have a ______ but has definite ______ and ______.
Ans: shape, density, mass.
(c) While freezing, the ______ of water is lowered.
Ans: density.
(d) ______ soil has pH 7.
Ans: Neutral.
2. Why is it said that –
(a) Air is a homogeneous mixture of various gases.
Ans: There are many constituent gases in the air. They are in the form of a mixture. The separate existence of each gas is not felt. The individual gases cannot be separated easily. Therefore, the air is said to be a homogenous mixture.
(b) Water is a universal solvent.
Ans: Many substances dissolve easier in water than in any other liquid. Therefore, water is said to be the universal solvent.
(c) There is no alternative to water for cleaning purposes.
Ans: Many substances can dissolve in water. Therefore, for bathing, cleaning utensils, and washing clothes, water becomes a very useful solvent. It is a cheap, easily available remedy for cleaning purposes. Therefore, it is said that there is no alternative to water for cleaning purposes.
3. What will happen if…..
(a) The amount of water vapour in the air increases.
Ans: When the amount of water vapour increases in the air, the humidity rises. The air becomes humid.
(b) Only one crop is grown repeatedly in the soil.
Ans: If the same crop is grown again and again, its texture disturbs and the fertility is lowered. The soil does not support the cultivation and the crops will not give proper yield.
4. With whom should I pair up?
Group ‘A’
(1) Air
(2) Water
(3) Soil
Group ‘B’
(a) Excretion
(b) Scattering of light
(c) Plasticity
Ans:
Group ‘A’
(1) Air
(2) Water
(3) Soil
Group ‘B’
(b) Scattering of light
(a) Excretion
(c) Plasticity
5. State whether the following statements are true or false.
(a) Sandy soil has low capacity for holding water.
Ans: True.
(b) The substance in which a solute dissolves is called a solvent.
Ans: True.
(c) The pressure exerted by air is called atmospheric pressure.
Ans: True.
6. Explain the picture in your own words.
Ans:
(i) In figure ‘a’, water is seen in the crevice over a land surface. This water is in liquid form.
(ii) In figure ‘b’, the same water is converted into solid ice.
(iii) As the temperature is decreasing, the water is freezing.
(iv) Since there is the formation of ice, that means the temperature is less than 4 °C.
(v) The water whose temperature is less than 4 °C becomes less dense, but its volume increases.
(vi) The water starts expanding, which is shown by the arrows in figure ‘b’.
(vii) Due to the anomalous expansion of water, the crevice in figure ‘b’ now looks bigger than the crevice in figure ‘a’.
7. Write answers to the following questions in your own words.
(a) How is light scattered by the air?
Ans:
(i) Air consists of a mixture of very fine particles of some gases, dust, smoke, and moisture.
(ii) When the light falls on the minute particles present in the air, these particles spread the light in all directions.
(iii) This is called the scattering of the light.
(b) Explain the various properties of water.
Ans: Water has the following properties:
(i) Fluidity: Water has the property of fluidity, due to which it can flow. Water is therefore used for transport and the generation of electricity.
(ii) Coolant: It can cool the heated equipment.
(iii) Universal solvent: Almost all things dissolve in water; hence, it is called a universal solvent.
(iv) Ability to perform body functions: Water takes part in the different biochemical reactions taking place in the body.
(v) Cleaning abilities: Water can clean almost everything. Thus, it is used in our day-to-day lives.
(c) Why is the density of seawater more than that of rain water?
Ans: Rainwater contains fewer dissolved particles compared to seawater, which contains a high amount of salt dissolved in it. This makes seawater much denser than rainwater.
(d) What is the importance of good soil structure?
Ans: Importance of good soil structure are:
(i) Good soil structure results in good soil fertility.
(ii) When the soil is of good quality, the roots get a sufficient supply of oxygen.
(iii) In such soil, the water drainage is good.
(iv) The plants grow well in such soil.
(e) What are the various uses of soil?
Ans: Various uses of soil are:
(i) Plant conservation: Soil helps plants grow.
(ii) Water conservation: Soil has a water-holding capacity. Therefore, water is available to us throughout the year.
(iii) Plasticity: Plasticity is the property due to which soil can be given any required shape. Therefore, various articles are made from soil. They are baked and made hard for longer use. e.g., storage of earthen pots, earthen lamps, idols, bricks, etc.
(f) What is the need and importance of soil testing from the point of view of farmers?
Ans:
(i) The farmer wants good produce from his crops.
(ii) By testing the soil, he understands the constituents of the soil on his farm.
(iii) Colour, texture, and the proportion of organic matter in the soil are tested by various testing procedures.
(iv) If there is any deficiency in the soil that is also found out, Measures to be taken to remove the deficiency are also suggested.
(v) The pH and the electrical conductivity tests are particularly useful in understanding the characteristics of soil.
(g) What is the importance of air in transmission of sound?
Ans: The importance of air in transmission of sound are:
(i) Air is the medium for the transmission of sound.
(ii) We are able to perceive the sound due to the air around us.
(iii) The sound waves travel through the medium of air and reach us.
(iv) In the absence of sound, we cannot hear the sound.
(v) Hence, air is most important for the transmission of sound.
(h) Why should a glass bottle completely filled with water never be kept in a freezer?
Ans:
(i) Due to the anomalous expansion of water, it expands while getting frozen.
(ii) When the temperature goes below 4 °C, the density of water starts decreasing, and at the same time, the volume increases.
(iii) The temperature in the freezer is always less than 4 °C. This causes the water to expand. Due to expansion, the bottle may burst.
(iv) A bottle is made up of glass. The broken glass pieces may cause harm.
(v) Therefore, the glass bottles should not be kept in the freezer after completely filling them.