CBSE NCERT SOLUTIONS

Question-1

State the different ways in which water is contaminated.

Answer:

The different ways in which the water is contaminated are:

i) Industrial waste: The harmful chemical wastes, released by the industries into water sources and pollutes the water.

ii) Sewage waste: kitchen, laundry and toilet release the waste materials that are responsible for polluting water.

iii) Agricultural chemicals: Excessive amount of pesticides and fertilizers are used by the farmers for enhancing crop production. Rains and floods contain harmful chemicals carried away to water bodies and pollute the water.

Question-2

What are the steps you could take to reduce air pollution?

Answer:

The following are the steps taken for reduction of air pollution:

i) We should avoid the usage of personal cars and opt public transport as much as possible.

ii) We should properly dispose the garbage and not burn it.

iii) For shorter distances, avoid vehicles.

iv) We should control the amount of emissions from household chimneys and vehicles.

v) We should replace our vehicle fuel, diesel and petrol by LPG and CNG.

Question-3

Do you agree that clean, transparent water is always fit for drinking?

Answer:

No, we don’t agree to the statement that clean water is always fit for drinking because water might appear clean but it may contains some disease causing micro-organisms and several other dissolved impurities. Hence, we advised to purify the water by boiling or by any purifying system before drinking it.

Question-4

Suppose in your town, you are a municipal body member. What are the measures taken by you that help your town to ensure the supply of clean water to all the residents?

Answer:

The following are the measures taken by us to ensure the supply of clean water to our town resident:

a) We clean the area around the water pipes.

b) The main water source has to be built in a clean surrounding, and should be maintained properly.

c) Chemical methods such as chlorination must be used for purifying water.

Question-5

Differentiate between pure air and polluted air.

Answer:

The composition of pure air contains 78% nitrogen, 21% oxygen and 0.03% carbon dioxide. Beside these, there are some other gases like methane, argon, ozone and water vapors’ are present. The air is said to be polluted, when the composition of air is altered by the addition of harmful substances or gases such as sulphur dioxide, carbon monoxide, nitrogen dioxide and particulate matter.

Question-6

What do you mean by the acid rain? What are its effects?

Answer:

Sulphur dioxide and nitrogen dioxide are the type of pollutants, which is released into the atmosphere by the burning of fossil fuels like diesel and coal. These pollutants react with the water vapours present in the atmosphere  to form nitric acid and sulphuric acid respectively. By precipitation, these acid come down and forms the acid rain.

Effects caused by the acid rain:

a) It destroys the crops.

b) Harmful for the building especially those made of white marble like the Taj Mahal.

Question-7

Among the following gases, which is not a greenhouse gas?

a) Sulphur dioxide

b) Carbon dioxide

c) Nitrogen

d) Methane

Answer:

c) Nitrogen

Question-8

What do you mean by the Greenhouse Effect?

Answer:

Greenhouse effect is the cause of global warming, i.e. overall increase in the temperature of the Earth. The greenhouse gases cause the greenhouse effect. Examples of greenhouses gases include methane, CO2 and water vapour. When solar radiation reaches the Earth, some radiations are absorbed by the Earth and then released back to the atmosphere. Greenhouse gases present into the atmosphere trap these radiations and do not allow the heat to leave. This helps our planet in keeping itself warm and thus helps in human survival. However, an indiscriminate increase for gases can lead to excessive increase in the Earth’s temperature leading to global warming.

Question-9

Write a brief note on Global warming.

Answer:

The increase in the average temperature of the Earth’s surface is known as Global warming. It occurs due to the increased concentration of greenhouse gases in the atmosphere. The greenhouse gases include methane, CO2, and water vapour. These gases trap the solar radiations released back by the earth, which results in keeping our planet warm and helps in human survival. However, an increase in these gases can lead to an increase in the earth temperature resulting in global warming.

Question-10

What are the threats to the beauty of Taj Mahal?

Answer:

The major threat to the Taj Mahal is the acid rain. When the acid rain falls on the Taj, which is completely made of marble, they react with marble to form a powder like substance which is then washed away by the rain.  This phenomenon is known as marble cancer. In addition, the soot particles emitted from the Mathura oil refinery located near Agra is leading to the yellowing of Taj Mahal marble.

Question-11  

Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

Answer:

An increase in the level of nutrients in water body leads to an excessive increase in the population of algae in the water body. When these algae die, they serve as food for de-composers. A lot of oxygen is utilized in this process, consequently leading to a decrease in the level of oxygen dissolved in the water body. This in turn causes fishes and aquatic organisms to die.

Question 1:

From the following pick out, which is not the member of the solar system?

a) A satellite

b) A comet

c) An asteroid

d) A constellation

Answer:

d) A constellation

A constellation is not the member of the solar system. These are the group of stars that forms a recognizable shape is known as Constellation.

Question 2:

Which is not a planet of the sun from the following?

a) Mercury

b) Earth

c) Sirius

d) Saturn

Answer:

c) Sirius

It is not the planet of the sun but it is a star.

Question 3:

What is the reason behind the phases of the moon?

a) Continuous changing of the distance of the moon from us

b) The thickness of the moon’s atmosphere is variable

c) We can see only that part of the moon which reflects light towards us.

d) Only the part of the moon’s surface is covered by the Earth’s shadow

Answer:

c) We can see only that part – of the moon, which reflects light towards us.

Moon does not have its own light. It is only be seen by us when sunlight falls on the moon and gets reflected towards us. So, we can only see the part of the moon on which the sunlight falls and reflects towards us.

Question 4:

Complete the following sentences:

a) Farthest planet from the sun is _________.

b) ________ are not actually shooting stars.

c) The planet whose color is red is _______.

d) ________ are the celestial body that revolves around the planet.

e) ________ are the group of stars that appears to form a pattern in the sky.

f) Asteroids are found between the orbits of _______ and _____.

Answer:

a) Farthest planet from the sun is Neptune.

b) Shooting stars are not actually stars.

c) The planet whose color is red is Mars.

d) Satellites are the celestial body that revolves around the planet.

e) Constellation is the group of stars that appears to form a pattern in the sky.

f) Asteroids are found between the orbits of Mars and Jupiter.

Question 5:

State True and False against the following sentences:

Answers:

The farthest planet in the solar system is Neptune.

During winters in the late evening, we can able to see constellation Orion. It seems to be the most beautiful constellation in the sky which can be seen through naked eyes.

The total number of planets in the solar system is eight; these are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

Stars are not the members of the solar system. The sun and the celestial bodies revolving around it in the solar system.

Question 6:

Match the followings from column A with column B.

Answer:

Question 7:

The planet Venus is found in which part of the solar system, if it is visible as an evening star?

Answer:

The planet Venus is found in the western part of the sky after sunset and is said to be known as an evening star.

Question 8:

Which planet is largest in the solar system?

Answer:

Jupiter is the largest planet in the solar system.

Question 9:

What do you mean by constellation? Name any two.

Answer:

The group of stars that forms a recognizable pattern in the sky is known as constellation.

Two constellations are;

I-Orion

II-Ursa Major

Question 10:

Draw the diagram that shows the relative position of prominent stars a) Orion b) Ursa Major

Answer:

a) Orion seems to be like a hunter. The three bright stars appear in the belt, while five bright stars are arranged in the form of a quadrilateral.

b) Ursa Major seems to be like a big dipper. There are four stars in the bowl of the dipper and three bright stars in the handle.

Question 11:

Name the two objects other than planets, which are members of the solar system?

Answer:

a) Meteors

Meteors are small celestial objects that are seen as bright streaks of light in the sky.  Due to the heat produced by the friction of the Earth’s atmosphere, the Meteors are burnt out while entering in, this causes the bright streaks in the sky. They are not planets.

b) Asteroids

The Asteroids are the collection of a huge number of small objects; gasses and dust are revolving around the sun. Between the orbits of Mars and Jupiter, they occupy the large gap. These are not planets. They are the celestial bodies and are known as Asteroids.

Question 12:

With the help of Ursa Major, how can you locate the pole star?

Answer:

For locating, the pole stars in the sky, first the big dropper or the Ursa Major constellation must be found out. The bowl of the big dipper consists of the four bright stars.

Imagine the two stars at the end of this bowl. Then make an imaginary straight line towards the northern direction connecting these two stars.

This imaginary line meets the star called Pole star. The length of the imaginary line from the bowl is about five times the distance between the two stars of the bowl.

Question 13:

Do you think that all the stars in the sky moves? Explain.

Answer:

No, the earth rotates on its axis from west to east. Therefore, all the stars in the sky (except the pole star) seem to move from east to west. With reference to Earth, pole star in the sky does not seem to move because it is located above the axis of rotation of the Earth in the north direction. It seems to remain stationary at a point in the sky.

Question 14:

Why is the distance between the stars expressed in light years? Clearly, elaborate the statement that “the star is eight light years away from the Earth.”

Answer:

The distance of the star from the earth and the distance between the stars are very huge. It is troublesome to express these distance in kilometer (km). Therefore, these huge distances are expressed in light years. One light year is equal to the distance traveled by the light in one single year. One light year is equal to 9.46 x 1012 km.

A distance of the star from the Earth is eight light year. This means the distance between them is equal to the distance traveled by the light in eight years, i.e. distance of the star is 8 x (9.6 x 1012) = 7.6 x 1013 km away from Earth.

Question 15:

The radius of Jupiter is 11 times bigger than the Earth. Calculate the ratio of the volumes of Jupiter and the Earth. So, how many Earth can fit the Jupiter?

Answer:

Let us consider Jupiter and Earth are two spheres with radii R and R’ respectively. Given in the question that radius of Jupiter is 11 times the radius of the Earth.

So, R’= 11R

Volume of sphere of radius r is given as = 43πr3

Volume of Earth = 43πr3

And, volume of Jupiter = 43π(R′)3=43π(11R)3=1331[43πR3]

The ratio of the volume of Jupiter and earth

Therefore, this ratio suggests that Jupiter can fit 1331 number of Earth in it.

Question 16:

Vikram has made the diagram of the solar system. Do you think the diagram he had made is correct?  If not, correct it.

Answer:

No, the diagram made by the Vikram is not correct, because in the solar system the planets sequence of their distance from the sun is like; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The mistake he had done is he changes the positions of the planets Venus, Mars, Neptune and Uranus. Besides this, he had shown in the diagram that the Asteroids belt in the gap between the orbits of Saturn and Jupiter. This is incorrect. The Asteroids belt is located in the middle of the orbits of Jupiter and Mars. The correct diagram of the solar system is given below: